Sanitizing the fresh water tank

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Well-known member
Nov 9, 2018
Molalla, Oregon
I am a new RV owner.  I found a great article in the library about sanitizing the RV water system.

I have what may seem as a dumb question (I am full of dumb questions):  Are there any "gotchas" or exceptions to the referenced procedure?  Has anyone experienced an unanticipated side effect? Can the bleach damage anything in the water system, for example, if the water isn't mixed sufficiently?  Will the bleach leave residue in a water filter that will result in bleach taste?

I have a 2003 Fleetwood Bounder 37U.  I just learned how to drain the tanks (hot and cold) including the low point drains.  I plan to do the bleach treatment next week.

Thanks in advance.

Rene T

Site Team
May 20, 2011
Farmington NH
No, the bleach will not hurt you. It's so diluted.  I've left mine in the system for over 24 hours before and nothing got damaged. You only need to leave it in there a couple of hours.  After a few days, it will dissipate anyways. 
I would run it through the filter also.
One other thing, no one here has dumb questions. If you don't know the answer, i's not dumb to as no matter how small it may seem to you.


Well-known member
Aug 9, 2012
Saint Johns, FL
this post got me curious... especially since I noticed some mildew growing in my fresh tank's vent tube the other day making me think I should sanitize the thing soon...
& I'm not in any way disputing the advice in that write I know that 1/4 cup to 15 gallon ratio is common advice for this and I have no doubt that it's grounded in some sort of science....
but the engineer in me couldn't remember what this hypo concentration is to be to sanitize a tank, so I googled it.  Found this on the clorox site

"If you have a tank with clear water that you simply want to make sure is safe to drink or use for human contact (hand washing, laundry, etc.), then you can follow the protocol for emergency disinfection of drinking water. In that case, the correct ratio of bleach is ? teaspoon Clorox? Regular Bleach2 per 10 gallons of water (or for a smaller size container, 2 drops per quart). Stir the bleach into the water and let stand 30 minutes. Properly treated water should have a slight chlorine odor?if not, repeat the dosage and let stand an additional 15 minutes.

To clean out a water tank, first thoroughly flush the tank using a bleach solution of 1 part Clorox? Regular Bleach2 per 150 parts water (a 500ppm bleach solution). I?m not sure of the size of your tank or how much bleach solution you will need, but here?s one example: if you want to make up 10 gallons of bleach solution, then you would start with 9 gallons + 15 cups of water, and then add 1 cup + 1 Tablespoon bleach. After flushing the tank with the 500ppm bleach solution, then rinse with a 10ppm bleach solution (1 teaspoon bleach per 10 gallons of water).
Read more at" basically a tad more than 1 cup bleach in a tad less than 10 gallons water..... call it 1 cup in 10 gallons, or 1.5 cups in 15 gallons.
the msds says this "clorox regular" is somewhere between 5-10% hypo solution by weight

Now I am far too many years out of chemistry class and haven't worked with this kind of math in many years...and don't have nearly enough energy to look up the densities of hypo and do all that conversion anyway.......
but based on the suggested 500ppm...and using an online calculator I found... and assuming standard household bleach at 5.25% sodium hypochlorite solution
...I come up with needing 2.4 cups per 15 gallons that online calculator wrong?

Well regardless....something between 1/4 cup and 2-1/2 cup per 15 gallons.... close enough for me I guess...;)

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