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Old 07-08-2024, 04:08 PM   #1
Winnebago Owner
Join Date: Apr 2018
Location: Roosevelt, MN
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Fresh water tank treatment, dual tanks

What is the best way to treat and fill dual 40 gallon tanks (80 total) so that they get equal treatment when de-winterizing? How much water should be filled before adding (all or part) shock treatment or whatever then continuing the fill? Dad is concerned that the tanks will get unequal treatment as we fill the rear. Here is a diagram of our (factory) connections (drain valve not shown on the pump draw).
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1997 Adventurer 34
Chevy P30 chassis
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Old 07-08-2024, 10:14 PM   #2
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Hi n0ukf,
I believe you must treat it as if it were one contiguous 80 gallon tank. I believe the turbulence of the water entering the tank will allow a good mixture of bleach and water to find its way into all areas of your plumbing. I would recommend this course of action:
  1. drain the hot water tank
  2. add 1 cups of bleach to the fill hose (this is cup of bleach per 15 gallons)
  3. fill the 80 gallons into the fresh water tanks
  4. run the hot water tap with the water pump to re-fill the hot water tank
  5. purge all other lines to make sure you smell bleach
  6. top-off the fresh water tanks
  7. let sit for four hours
  8. drain the hot water tank
  9. drain the fresh water tanks
  10. refill the fresh water tanks
  11. run the hot water tap with the water pump to re-fill the hot water tank (or just use City Fill)
  12. purge all other lines to make sure you no longer smell bleach
I do not believe you should run any stronger mixture of Bleach. If you feel your tanks are not clean, then repeat the process.
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Old 07-09-2024, 07:39 AM   #3
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When thinking of water and making it safe to drink, it is important to keep in mind that any specific amount to use can only be an estimate!
One of the big issues on not being precise is that it is impossible to tell how much we need. The bleach will react with any organic materials it finds. So how much is there going to be in the tank at any time is not something we can judge!
In our RV it will depend on too many variables to even begin, so we set a standard that is hoped to be enough and that is often way too strong to drink.
Any water we drink has a certain amont of bacteris left in it and given time that will multiple. How fast and how much, depend on things like what treatment was left in the water in the tank and how warm as well as how long.
Much like bottled water that has a specific length of time for it to be safe, any water will go bad under the right conditions.

Bleach is sold, shipped, and stored in plastic and has been for decades without harm. That leaves me to simply want to make sure I get enough to do the job and then drain and flush it to get the chlorine levels back down to the normal drinking water levels.

Kind of like asking how many buckets of mud will be left after a flood? No point in trying to be precise! Just make sure you get it all!

For the two tanks, if you add the bleach first and then the water, some will move to the second tank while some stays in the first and it is not at all critical as it will mix and change as you drive. Since one of the places where fungus and mold may grow is the top of the tank, I like to move the RV to slosh some up there before draining. Maybe not "required" but I feel better if I know bleach water has gotten to all the parts.

Then if you also use treated city water from a good source, that water will have chlorine residual left to take care of any small amounts missed. Old bottled water is far more hazard than freshly treated RV water, as the bacteria will have time to regrow after the water is put in the bottle and stored!
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Old 07-09-2024, 11:28 AM   #4
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Location: Roosevelt, MN
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Originally Posted by Morich View Post
Then if you also use treated city water from a good source, that water will have chlorine residual left...
No city water, private well. It's been well over a decade since we've tested it (last was after a flash flood and we bleach-treated it at that time).

Anyway, Dad is far more concerned about equal/unequal treatment of the dual tanks than I am, and we carry a few gallons separately for drinking anyway (til we find something that works to keep the system palatable for more than a day or two).
1997 Adventurer 34
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Old 07-12-2024, 09:50 PM   #5
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It will not harm anything to double-dose with bleach. If after rinsing the tanks to remove the bleach, it still smells and tastes of bleach, do the same thing but using baking soda to remove bad tastes and freshen the entire RV plumbing system.
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