Black Tank Draining Sewer Smell

[treimche]

Can someone help me identify where/how the smell enters the interior of my 1999 Chieftain when I drain the black tank? I have already replaced the wear parts in the toilet with a new flush valve, waste ball, waste ball seal, closet flange seal, etc. The waste ball seal in the toilet will hold water for hours and hours on end. I have replaced the vent caps under both sinks with these https://www.amazon.com/dp/B000KKSP52...roduct_details but the issue persists. I'm also using the Happy Campers powder mixed in water after each time I empty the tanks.

It sucks when I drain the tank because I have to open the windows and turn on the vent fan in order to clear the stink from the RV. Being in SW FL, this is not ideal since it's always hot here.

Could there be an issue with the vent going to the roof? Other ideas of where to look?

[Ray,IN]

You're on the right track. The black and gray tank vents on the roof should be above the roofline by approx. 2-3", covered by a rain cap. If the vent pipe is not secured into the top of the tank it can vibrate down below the roofline and vent into the attic space_so to speak.
There should be 1 screw holding the vent cap onto it's base. Remove that screw and observe the pipe height, it should be level with the top of the base, and fit tight.

[treimche]

Originally Posted by Ray,IN

You're on the right track. The black and gray tank vents on the roof should be above the roofline by approx. 2-3", covered by a rain cap. If the vent pipe is not secured into the top of the tank it can vibrate down below the roofline and vent into the attic space_so to speak.
There should be 1 screw holding the vent cap onto it's base. Remove that screw and observe the pipe height, it should be level with the top of the base, and fit tight.

This is the style of vent on the roof of my RV. Not this exact one, but something similar. I'll have to look at it closely and see if the pipe is still connected to it. https://www.amazon.com/Rotating-Sewe...399315439&th=1

[treimche]

Reviving this. The smell seems to be coming out of the area underneath the sink and it smells really strong by this vent that is next to the doorway. If there were pics of how the black tank venting was all laid out this would help me a lot, but I don't know where to find something like that.

[IOS 3]

Your gray tank valve is closed when dumping black, correct? And the gray tank valve is in its original location upstream from the "y" where black and gray join the main dump line. Correct? Just want to eliminate this as a cause...

Next, in your rig does everything except the toilet drain to gray? If yes, the only black tank vent you will have should be on the roof.

[Marine359]

You’re certain that smell is not from the gray tank? Those odors can waft back into your under-carriage pipes when either valve is opened. First, rinse black tank until effluent is absolutely clear. Just to make sure, it doesn’t hurt (we do it annually), put 1/4 cup of Dawn, 1 cup vinegar, and at least three gallons of water into the gray tank. Do the same to black tank, except substitute 1/4 cup bleach in black tank. Drive around awhile to get washing machine effect. A bag of ice down the toilet while driving helps. Dump black first and rinse the tank until absolutely clear. When dumping gray, it should be absolutely clear as well. Bad stuff can grow in your gray tank even when it’s empty, and it won’t go away with emptying the tank alone.

[Morich]

Three main sources of really foul smells on RV, so I would want to start by ruleing out any I can.
there is the black as you suspect but our noses are not well tuned for that sort of thing, so it may be other smells.
Grey can be really bad and confuse us but somewhat easy to rule it out as there are limited ways the smell gets inside.
I would try to rule the grey out by capping off the inside sources like the air admittance valves. you've changed them and we might tell ourselves we are now good but bad stuff can be new!
I would have to think about exactly when an how we get the smell but if only as you dump the black, I would first plug the grey points where it might enter. A simple job of shrink wrap, etc and a few rubber bands to hold it airtight over the air valves before dumping the black would help. Before doing this test, be aware that this valve is what keeps the water in the traps from being sucked out, so make sure to have water in the traps AND the shrink wrap on before trying the black dump!

Black smell getting to that location next to the door seems a really hard thing to see happens, due to location of tank and pipes so far away.
Plumbing diagrams here:
https://www.winnebago.com/Files/File...m/Plumbing.htm
It can also be possible to get a different view of them here on the parts:
https://catalog3d.winnebagoind.com/menu/Parts.htm

But , if not grey smell, I would jump to thinking there is a dead animal in or near the vent? That would be a return air vent to the furnace and they are often simply flex duct that is easy for mice, chipmunks, etc to chew through and use as home.
Maybe you only smell it at certain times but what happens if you turn the furnace on? If it stinks you out, I would consider that a sure sign that something is in the duct and you may only pick it up at certain times!

If you put that small fan/blower against one of the far heat ducts and blow in, does it give you massive smell coming out the vent by the door? That might say there is a dead animal in the duct at some point!
What do you get if you take the vent cover off and look inside? Any signs that rats, mice, chipmunks are living there?

I would not look further at the vents as the black and grey vents are combined and any smell from one should also be picked up from the other. They both go out the roof on the same pipe.

[Marine359]

Good post Richard

[Morich]

With a bit more time, I'm able to show my thoughts on why I suspect it is NOT black water? Of course it is all a guessing game until we actually find and fix the problem but this is why I would move away from thinking black water smell.

The black tank is in the rear and there are two holes which might leak odors. One is the stool and OP has gone there to look at seals, etc. The other is the connection between the vent stack and tank. But if we assume the vent is still drafting and pulling air up as it should, any smells right at the connection to the tank would tend to move up the pipe and outside. That connection is also quite a long way from the front door vent where they pick up the smell being strong. Possible, yes but less than probable in my thoughts.
Click this snip to get the better view!


I might think a leaking air admittance valve under the sink might be suspect as it is very near the same spot as the vent, so I would want to cover that as well as the one under the vanity in rear, just because it is simple to do and rule out those suspects?

What WOULD fit if I knew my nose was not great at telling the difference is something dead in the furnace vents, either hot or cold as they are an open connection and lead all through the RV, from front to back!

Some details would need to be checked but I might see it easy enough for the OP to go out and open the wet bay to dump, that side having a breeze to blow in the bay and up through the floor, making the vent really smell as the odor comes up inside?

Being in warm country, have they been running the furnace yet?

Too bad we don't have an odor detector like we have to measure and test for voltage!!

So we get to play the guessing game!

[treimche]

Originally Posted by IOS 3

Your gray tank valve is closed when dumping black, correct? And the gray tank valve is in its original location upstream from the "y" where black and gray join the main dump line. Correct? Just want to eliminate this as a cause...

Next, in your rig does everything except the toilet drain to gray? If yes, the only black tank vent you will have should be on the roof.

To answer all of your questions:
Yes the gray tank is closed when dumping black tank.
Yes the gray tank valve is in its original location upstream from the "y" where the black and gray join.
Yes everything except the toilet drains to gray tank.

[treimche]

Originally Posted by Marine359

You’re certain that smell is not from the gray tank? Those odors can waft back into your under-carriage pipes when either valve is opened. First, rinse black tank until effluent is absolutely clear. Just to make sure, it doesn’t hurt (we do it annually), put 1/4 cup of Dawn, 1 cup vinegar, and at least three gallons of water into the gray tank. Do the same to black tank, except substitute 1/4 cup bleach in black tank. Drive around awhile to get washing machine effect. A bag of ice down the toilet while driving helps. Dump black first and rinse the tank until absolutely clear. When dumping gray, it should be absolutely clear as well. Bad stuff can grow in your gray tank even when it’s empty, and it won’t go away with emptying the tank alone.

I rinse probably 10-20 extra gallons of water through the black tank each time I empty it. Then I close the black tank valve and pump 10-15 gallons into the black tank and drain again. I have used a Thetford tank cleaning product a couple of times. It's just one that you dump the bag of stuff down the toilet, then fill the black tank with water until almost full, let it sit overnight and dump in the morning.

I haven't driven the RV around with cleaning products in the tank because we are hooked up and living in it at a campground. I do have the Happy Campers Extreme Tank cleaner to use once our stay here is done next month. I also use the Happy Campers tank treatment after each time I empty the tank.

[treimche]

Originally Posted by Marine359

You’re certain that smell is not from the gray tank? Those odors can waft back into your under-carriage pipes when either valve is opened.

I have tested my theory by only draining the gray tank, and there is no smell from the gray tank when I have to dump it. But a few minutes after dumping the black tank, its like I jumped into a sewer.

Speaking of the gray tank, I sometimes leave the gray tank valve open if I know we are going to be taking showers/washing dishes/etc a lot. I forgot it open for a few days at one point and never had any odd smell or anything.

[treimche]

Originally Posted by Morich

Three main sources of really foul smells on RV, so I would want to start by ruleing out any I can.
there is the black as you suspect but our noses are not well tuned for that sort of thing, so it may be other smells.
Grey can be really bad and confuse us but somewhat easy to rule it out as there are limited ways the smell gets inside.
I would try to rule the grey out by capping off the inside sources like the air admittance valves. you've changed them and we might tell ourselves we are now good but bad stuff can be new!
I would have to think about exactly when an how we get the smell but if only as you dump the black, I would first plug the grey points where it might enter. A simple job of shrink wrap, etc and a few rubber bands to hold it airtight over the air valves before dumping the black would help. Before doing this test, be aware that this valve is what keeps the water in the traps from being sucked out, so make sure to have water in the traps AND the shrink wrap on before trying the black dump!

Black smell getting to that location next to the door seems a really hard thing to see happens, due to location of tank and pipes so far away.
Plumbing diagrams here:
https://www.winnebago.com/Files/File...m/Plumbing.htm
It can also be possible to get a different view of them here on the parts:
https://catalog3d.winnebagoind.com/menu/Parts.htm

But , if not grey smell, I would jump to thinking there is a dead animal in or near the vent? That would be a return air vent to the furnace and they are often simply flex duct that is easy for mice, chipmunks, etc to chew through and use as home.
Maybe you only smell it at certain times but what happens if you turn the furnace on? If it stinks you out, I would consider that a sure sign that something is in the duct and you may only pick it up at certain times!

If you put that small fan/blower against one of the far heat ducts and blow in, does it give you massive smell coming out the vent by the door? That might say there is a dead animal in the duct at some point!
What do you get if you take the vent cover off and look inside? Any signs that rats, mice, chipmunks are living there?

I would not look further at the vents as the black and grey vents are combined and any smell from one should also be picked up from the other. They both go out the roof on the same pipe.

I can definitely try your trick for sealing off those 2 air admittance valves. The smell doesn't ONLY come from that vent by the door, but that's where it seems strongest. The bathroom will stink too. Under the bathroom vanity, and under the kitchen sink, both stink badly after dumping the black tank, so it seems like there could be air being pushed back through those air admittance valves somehow?

I don't think the dead animal theory is bad at all, but I haven't even turned the heat on in the RV once since buying it in May, plus we have some of the floor vents covered to help keep bugs out. The bad smell ONLY happens after dumping the black tank. It's rarely windy here, so it doesn't seem that the smell will matter depending on which way the breeze is going.

I'm starting to think I need to make sure the vent stack that come off the tanks to the roof is still connected and in place. I just don't know how to access it.

[Morich]

Just as a "thinking" idea?
What I see is this, whether anywhere close is not a sure bet!


Vent stacks are just mini-chimneys that should always have a small flow of air rising (warm air going up?) so if the traps have water to seal them and the air valves are good the air from any tank should go up and out as the green line?
To get air from black to grey and into the RV, it should have to fight the upflow and then the trap and valves should be closing it off before getting inside?
The only connection between black and grey should be the venting and main dump drain, so I don't see that as likely?
I see a third trap that is labeled with 11. Any chance that trap is dry so it would not be sealed from odors coming up?

Yes, easy to see that any smell getting into the furnace ductwork is open to going either to the cold air return or the heat ducts as they are pretty much an open tube going to lots of points in the RV! In theory, they should be a pretty airtight thing when new but that still leaves lots of ways for smell to move around the RV!

Then if all else, is there any chance of the main dump drain plumbing plastic having a crack where I marked as purple?
Any way top look as far back as the tank fitting?
Something odd like when you push or pull the black drain handle it opens the crack and a bit of black gets dumped but there should always be standing black water, so does pulling open a crack and letting go, it closes?

Getting into spacy thinking but would a cell phone inspection camera like on a long cord let you look back into any hidden spot for signs of leaking over the long haul? Others on the forum have suggested they have found them handy for looking in hidden spaces?

[treimche]

Originally Posted by Morich

Just as a "thinking" idea?
What I see is this, whether anywhere close is not a sure bet!
Attachment 187802

Vent stacks are just mini-chimneys that should always have a small flow of air rising (warm air going up?) so if the traps have water to seal them and the air valves are good the air from any tank should go up and out as the green line?
To get air from black to grey and into the RV, it should have to fight the upflow and then the trap and valves should be closing it off before getting inside?
The only connection between black and grey should be the venting and main dump drain, so I don't see that as likely?
I see a third trap that is labeled with 11. Any chance that trap is dry so it would not be sealed from odors coming up?

Yes, easy to see that any smell getting into the furnace ductwork is open to going either to the cold air return or the heat ducts as they are pretty much an open tube going to lots of points in the RV! In theory, they should be a pretty airtight thing when new but that still leaves lots of ways for smell to move around the RV!

Then if all else, is there any chance of the main dump drain plumbing plastic having a crack where I marked as purple?
Any way top look as far back as the tank fitting?
Something odd like when you push or pull the black drain handle it opens the crack and a bit of black gets dumped but there should always be standing black water, so does pulling open a crack and letting go, it closes?

Getting into spacy thinking but would a cell phone inspection camera like on a long cord let you look back into any hidden spot for signs of leaking over the long haul? Others on the forum have suggested they have found them handy for looking in hidden spaces?

In that diagram, the 2 #11s would be the drain from the shower and the drain from the bathroom sink?

So if the pipe going up to the roof vent, or the roof vent itself is plugged somehow, would this cause the stink to enter the RV by pushing through the vent caps under each sink?

How do I check that pipe and roof vent? Just get up there and try to remove the vent?

I should take a video next time I empty the black tank. It's kinda weird. It seems like when I pull the valve open, it will start to drain, but then after a couple of seconds it sounds like something opens or releases, then it starts draining faster. Maybe there's a venting issue?

One more thing to mention, one time when I was filling the black tank via the rinse valve, once it got over 30 gallons of water (I have an inline Save A Drop water meter) I could hear water leaking out from somewhere around the black tank, so I immediately shut the water off and pulled the black tank drain valve. From what I have seen, the black tank is supposed to hold 40 gallons. Maybe this is related? Maybe the black tank has 10 gallons of "stuff" stuck inside?

[Morich]

Well, we can get into all kinds of questions and not have good answers!
How well do you know this RV? Is it one you've had for a while and suddenly the smell is a problem or new to you and finding the smell about the first time using it?

What I'm getting at is whether it might be something that has happened new or something where somebody sold you their problems?
Then that can get into what you might know about the vent on the roof. Is the cap still there? Any chance something has built a nest to stop it up?
Wasps will sometimes build in the plastic vent pipe on newer furnaces that use a blower to blow the fumes out sideways instead of venting out a chimney. I had a problem with one where the wasps built a nest just inside the end of the pipe and it got so big and curved just to fit the pipe and the furnace would not light because it was built to not start until airflow was good.
No chance somebody dropped a rock in the vent?

The vent should just be an open pipe for air to blow up and out, sucking the odors out above the RV.

The air vent things are just there to keep the water in the traps. The water should stay in the trap and that water makes the seal to keep smell out of the RV. If the air vent sticks, water going down the drain as we drain it can make a suction and suck enough water out of the trap that it doesn't seal that opening and then we get fumes coming in.

You only have two air vents but the one takes care of two traps on that combined line.

Am I right that this happens as you dump and not all the time smell bad?
The hard part is figuring how you can get the bad smell when you dump but not all the time when not dumping!
What made me think of something that moves as you dump was maybe pulling move the pipe and lets some leak and then when you turn loose of the handle, it kind of moves back to close up the leak??

How much does it wiggle?

There is a rubber fitting shown where the black drain pipe connect at the side of the black drain. Possible that rubber is loose or getting old and brittle? Maybe a metal clamp not holding it on tight?


Bet it's not handy to see that spot!
Any chance you might spot where black has been leaking a little out there when you drain? Seems like leaking enough to smell bad inside, it would be enough to make a stain where it dribbled down, even if not enough to really see on the ground?

Lots more questions than answers!

[treimche]

Maybe someone can help make sense of something I tried. The last 2 times I emptied the black tank, I had the g/f flush the toilet while I opened the black tank drain valve. This has eliminated at least 90% of the smell somehow. My suspicion is that the vent is somehow clogged, and flushing the toilet allows the toilet to act as a vent, letting air into the tank so it drains easily. Does this make any sense to anyone who is still following?

[Morich]

I think you are getting close!
I might go for testing the vent on the roof. But I might start with doing it from the ground as the easy way.
Can you figure a "home made" way to make some way to hold a house vacuum hose tight enough to the black drain to show good air flow in/out of the roof vent? With the tanks empty, air should flow easily without any restriction from RV roof to the drain.

You may have something like a wasp nest built in the vent? Maybe a bird started a nest and you have it half stuffed with sticks and grass?

One problem with this is that the vent might be totally stopped and the vac still get air by sucking it in through the air vents at sink and vanity? So if it seems to struggle and then suddenly comes free, check to see if there is still water in each trap. putting a stopper in the sink drains might avoid this?
If you have a vac like a shop vac that has an outlet where you can connect the hose to blow, rather than suck, maybe try blowing to see if anything might come out the roof?

Last idea might be to go to the roof and run wire, etc down to see if you could snag something out of the vent?

I think you are getting close and air is not moving right to get in and out of the vent in the right way.
Did you ever use one of the old thermos jugs that you put water and ice in and had a spout at the bottom to get drinks? They worked lots better if you cracked the lid open to let air in!