Gray Tank Capacity

[Bitzer]

Hi all. I decided to finally join this forum when I bought my latest motorhome, a 2021 Winnebago Adventurer 27N. I've been browsing as a guest for years - this is a valuable resource for RVers. That said, I've got a problem about which I could use some advice:

The specifications for the 2021 27N say the grey tank capacity is 54 gallons, which is more than our old motorhome by about 10 gallons. However, we've noticed that the gray tank fills up more quickly than we expect on this rig, AND the tank sensor shows the tank as only 2/3 full when it starts backing up into the shower pan.

So ... last weekend after dumping both black and gray tanks completely, we parked the motorhome in the driveway, leveled it, and performed a test. We poured water down the shower drain in 2 gallon increments, let the water drain completely, and then noted down the sensor readings each time.

The sensor jumped from empty to 1/3 full at 18 gallons, then jumped to 2/3 full at 36 gallons, and also stopped draining at this point. Adding more water just filled up the shower pan. Dumping additional water down the bathroom sink and the kitchen sink just filled up those drain pipes but didn't move the sensor. I've repeated this experiment twice at different times and gotten the same result both times.

I have pulled the waterless trap under the shower; it's not plugged. I have climbed up on the roof, popped the vent cap for the gray tank and shone a flashlight down the ten foot tube; it isn't plugged. Other than the very unlikely possibility that Winnebago installed the wrong tank in my motorhome, I'm running out of ideas. All I can think of is maybe somehow air is getting trapped in the tank and preventing it from filling up completely?

Is this even possible? Ideas anyone?

[Morich]

Welcome to the group, lots of info and ideas here!
Stepone when I get a different RV,is to find out what I've bought and with the newer Winnebago, they give some great tools.
This interactive parts section is my fav as it allows me to find out all kinds of things without leaving my chair to crawl under and through the RV or guess:
https://catalog3d.winnebagoind.com/menu/Parts.htm

Choosing the right exact year, make, model and even the serial number on some can get right down to things like how the tanks set as well as size.

I did not sort to serial number so some guess but I think I might see an explanation of what you are finding.
First thought is that your RV has a tank which seems to be wide and long but somewhat shallow. More like a shallow pan instead of a bucket?

You may want to go to the full picture to take a better look or click on these pictures for what I think I see?

https://catalog3d.winnebagoind.com/2020/331071.htm

When tilted in any direction front/back or left right it will change the way the water level fits into the tank and if there is a small tilt with front right higher, it definitely makes the corner of the tank where the shower drain sets become the lowest point.

This shows far more when we have shallow versus deep tanks. The space may be there but we can't get the use due to the way the water runs?

[Bitzer]

Yeah, Morich, I have also found those online CAD/CAM type displays on the Winnebago online parts site to be very useful! A pretty handy resource.

Your idea about the relative 'shallowness' (is that a word?) of the tank is an interesting one. This leads me to a few avenues to explore:

(1) Measure the actual depth of the tank; I suspect it's in the 9-12" range. Maybe do some math to see how sensitive to level a tank of that depth would be, i.e., how out of level does it have to be to have a noticeable effect?

(2) With the RV automatically leveled, I could climb into the storage compartment with access to the top of the gray tank and put a level on the top of the tank - is it level too?

(3) Either during another experimental session or when the water backs up again, whichever happens first, I could try manually tweaking the leveling of the motorhome to see if the capacity changes much. If I'm interpreting the drawing correctly, it looks like (for the gray tank), elevating the driver's side rear of the motorhome just slightly might make a backup into the shower pan drain back into the tank.

[Morich]

Not at all sure I recommend it and I have never gotten to that point but there are some really "odd" ways to deal with grey tanks that get full too soon.

One that I know of is having a storage tub to drain some off into, add a small pump to that tub and pump it into a container in the truck bed to haul to drain into a drain!

Way too much for us as we never get into staying that long or the moving is not enough to bother going to that much pumping but the fellow who worked that out did have lots of "stuff" he set out around the RV and it was a real bother for him to pull up and go dump! We often had dinner on the table before they got done setting up.
Different ways of roughing it!

[Bones2003]

Bitzer, I am following this thread so I hope you keep posting about what you discover and that others will chime in. I will have to do some testing because my gray tank seems to fill pretty quickly. It is rated at 57 gallons but I am suspicious about that. The bathroom sink drains into the gray tank on my new RV while my it drained into the black tank in my old RV.

As I understand it you have two issues.
1) Your tank capacity appears to be 38 gals but it should be 54 gals. Are you sure the tank was really empty when you started? Hard to believe you could miss 18 gallons though when draining. From the drawing that Richard provided in post #2 above, raising the front and the passenger side should give a full drain.
2) Your tank sensors increment to 1/3 full and 2/3 full but not to FULL. Interesting that you put in 18 gals and got 1/3 because 18/54 is 1/3 (same for the 36 gals and getting 2/3). Seeing those numbers, everything looks great until the shower starts to back up!

Do you have access to measure the physical dimensions of your tank and then calculate how many gallons would fit into that volume? 1 cubic foot is 7.48 gallons.

Keep us posted.

[MadMaxWinny]

Side note: on very shallow tanks, sensor accuracy is nearly magic. I've got a 165 gallon "belly tank" on my boat, and the bloody thing reads "full" at 30% empty, "half" at 60%, and 3/8 at bone dry. I've had similar experience with other tanks, even one the ones I had full access to the mechanical sensor for adjustments. Newer electronic sensors are more dependable, but (as already mentioned) the slightest tilt out of level can cause wildly different readings.

[powercat_ras]

I have a 2015 Vista 27N and can confirm that it has a 53 gallon capacity grey tank as specified in the 2015 Vista 27N brochure. So far as I can tell, the grey and black tank type size and location and the drain runs are identical going on up to the current model year.

As you may already know, the Adventurer and the Vista LX before it were just re-branding of the 2015 Vista 27N and are still exactly the same "bones" as before but with some upgraded cosmetic items. Major upgrades were change from 30A to 50A shore power, bigger generator, 2 roof top AC, and the front window power shade.

You can see the side of the grey tank and the three side tank level sensors looking into the two front passenger side basement compartments. Personally I have not had a problem with the tank overflowing into the shower pan before the Full indication is shown.

In the 2015 model year they still used the One Place control panel with the E 1/3 2/3 and Full LEDs and not the digital display.

[powercat_ras]

Some other thoughts ...

There is supposed to be foam support under the gray tank, perhaps that was not installed correctly at the factory and the tank is not laying flat on the chassis structure as engineered.

The tank sensors are on the passenger side wall of the tank. If the RV is not level and the driver's side is lower than the passenger side, then you won't get the full 53 gallon capacity and the grey water will back up into the shower well before you get 53 gallons into it, and since the sensor side of tank is higher than the other side the level indicators won't be accurate. So maybe your leveling system is not correctly calibrated to level the 27N correctly.

[Oakprk]

Originally Posted by Bitzer

Hi all. I decided to finally join this forum when I bought my latest motorhome, a 2021 Winnebago Adventurer 27N. I've been browsing as a guest for years - this is a valuable resource for RVers. That said, I've got a problem about which I could use some advice:

The specifications for the 2021 27N say the grey tank capacity is 54 gallons, which is more than our old motorhome by about 10 gallons. However, we've noticed that the gray tank fills up more quickly than we expect on this rig, AND the tank sensor shows the tank as only 2/3 full when it starts backing up into the shower pan.

So ... last weekend after dumping both black and gray tanks completely, we parked the motorhome in the driveway, leveled it, and performed a test. We poured water down the shower drain in 2 gallon increments, let the water drain completely, and then noted down the sensor readings each time.

The sensor jumped from empty to 1/3 full at 18 gallons, then jumped to 2/3 full at 36 gallons, and also stopped draining at this point. Adding more water just filled up the shower pan. Dumping additional water down the bathroom sink and the kitchen sink just filled up those drain pipes but didn't move the sensor. I've repeated this experiment twice at different times and gotten the same result both times.

I have pulled the waterless trap under the shower; it's not plugged. I have climbed up on the roof, popped the vent cap for the gray tank and shone a flashlight down the ten foot tube; it isn't plugged. Other than the very unlikely possibility that Winnebago installed the wrong tank in my motorhome, I'm running out of ideas. All I can think of is maybe somehow air is getting trapped in the tank and preventing it from filling up completely?

Is this even possible? Ideas anyone?

Hi Bitzer, I've been battling my grey water tank since my 27N was new in February 2019. I took it to the dealer and they claimed that they leveled it in the yard and filled it to full on the gauge without any backups. It didn't change my experience.
The problem isn't that the tank is too small or that it's not level. The problem is that it's not venting. You can confirm that by removing one of the vent check valves in the down-pipe of the bathroom or kitchen sinks and you will feel/hear the whoosh of air as the tank vents and see the shower pan (or sink) drain.


I did open the access cover to the top of the grey tank, loosened the clamp holding the vent pipe and (after removing the roof vent cap) pulled the pipe out of the tank. I couldn't tell if it was extending too deep into the tank but I inserted it back into the seal and added a clamp to hold it from slipping further in (which it didn't have). Sadly, it didn't seem to make much of a difference in the gauge readings. The grey water will start backing up at 2/3 full.

I also thought the placement of the tank sensors didn't look right so I had the dealer lower the 2/3 sensor. They couldn't move it down much without removing other tie-downs but that didn't seem to make any difference. I now live with it and just plan on emptying the tank when it shows 2/3 or remove a vent check valve if I want to extend my dump time.

[Oakprk]

Originally Posted by powercat_ras

Some other thoughts ...

There is supposed to be foam support under the gray tank, perhaps that was not installed correctly at the factory and the tank is not laying flat on the chassis structure as engineered.

The tank sensors are on the passenger side wall of the tank. If the RV is not level and the driver's side is lower than the passenger side, then you won't get the full 53 gallon capacity and the grey water will back up into the shower well before you get 53 gallons into it, and since the sensor side of tank is higher than the other side the level indicators won't be accurate. So maybe your leveling system is not correctly calibrated to level the 27N correctly.

As long as the vent isn't obstructed water won't back up into the shower pan even if the driver side is low, Water will seek it's own level as long as the tank is vented, Since the shower pan is higher than the water level in the tank, it will continue to drain.

[Clydesdale]

I had the exact same thing with my 2017 Forza 34T. After installing a new tech edge tank monitoring system, I was calibrating it to discover it didn't hold what it should have either. In my case I discovered there is a connection for the bathroom sink/vent near the top center of the tank. During assembly they pushed the pipe down so hard from the sink they deformed the top of the tank down nearly 3 inches. That trapped air in the tank and dropped the capacity. We boondock alot so I went to the extreme of removing the tank, painting the top black, setting out in the sun to soften, inflating it with a couple pounds of air pressure, then letting it cool that evening. It worked. I was able to cut a couple of inches off the vent pipe when I re-installed.

[CJBROWN]

Use less water. Problem fixed.

[danhannah]

Wow Morich, that reasoning is brilliant.

I've not much to add here, except that my shower starts to flood almost exactly when the full light comes on. Now I am curious how much water that is...

Couldn't a guy just figure out his gpm from the hose bib at the house, using a five gallon bucket, and measure the tank that way?. or would that be inaccurate.

[Upinsmoke]

I have a friend who wanted to check his capacity and rather than run buckets of water, he installed an inexpensive flow meter on his garden hose and it worked like a champ. Just an fyi,

[Bitzer]

Powercat ras,

They still have the 4 LEDs. Looking at the side of the tank where the sensors are mounted, I can see that they did a somewhat sloppy job of spacing them up the side of the tank. The 2/3 sensor is almost completely overlapped with the full sensor.

Does anyone know if those little sensor squares are just glued onto the exterior of the tank wall? If there is no actual physical hole in the tank wall underneath the sensor, then maybe I could 'unglue' it and move it down a bit.

[Bitzer]

Upinsmoke,

Yep, after filling the tank the hard way with a 2 gallon pitcher, I found one of those flow sensor gadgets for $20 on Amazon. It worked like a champ, and also verified my earlier findings.

[Bitzer]

Bones2003,

Good idea about calculating the capacity from the external tank dimensions. I will have to give that a try when I get the RV back from the Ford dealership in hopefully ONLY 3 weeks time. (Dash A/C problem, another nightmare experience.)

[Bitzer]

Originally Posted by Oakprk

Hi Bitzer, I've been battling my grey water tank since my 27N was new in February 2019. I took it to the dealer and they claimed that they leveled it in the yard and filled it to full on the gauge without any backups. It didn't change my experience.
The problem isn't that the tank is too small or that it's not level. The problem is that it's not venting. You can confirm that by removing one of the vent check valves in the down-pipe of the bathroom or kitchen sinks and you will feel/hear the whoosh of air as the tank vents and see the shower pan (or sink) drain.


I did open the access cover to the top of the grey tank, loosened the clamp holding the vent pipe and (after removing the roof vent cap) pulled the pipe out of the tank. I couldn't tell if it was extending too deep into the tank but I inserted it back into the seal and added a clamp to hold it from slipping further in (which it didn't have). Sadly, it didn't seem to make much of a difference in the gauge readings. The grey water will start backing up at 2/3 full.

I also thought the placement of the tank sensors didn't look right so I had the dealer lower the 2/3 sensor. They couldn't move it down much without removing other tie-downs but that didn't seem to make any difference. I now live with it and just plan on emptying the tank when it shows 2/3 or remove a vent check valve if I want to extend my dump time.

Oakprk,

I have wondered if there was a problem with venting. I pulled off the grey tank vent cap on the roof and shone a flashlight down there. It isn't plugged; when the tank is empty I can see what looks like the bottom of the tank.

I'm unaware that there are vent check valves on the sinks; you're talking about something different from the simple trap under each sink, right? Can you give me a hint as to how to access the check valves?

[Bones2003]

Bitzer, the devices that Oakprk calls "vent check valves" are actually air-admittance valves or Winnebago calls them mechanical vents. If you look at Richards first photo in post #2 above, they are the blue items on top of the TEEs next to the sink traps. I don't think they are glued in - just pressed fit or screwed in - so you can easily pull one off and test it as Oakprk mentioned.

Also the tank sensors are generally just stuck on the side of the tank with double stick tape. You can use a length of dental floss as a type of saw to cut through the tape. On other forums, people have stuck them back on with 3M tape after cleaning the old tape off. Apparently, you don't really have to worry about the thickness of the tape.

[Bones2003]

Bitzer, see post (EDIT) #6 in this thread for more info on the sensors:

https://www.winnieowners.com/forums/...or-364385.html