Friday, June 2, 2023


How do I sanitize my RV’s fresh water tank through the filter?

Dear Dave,
I want to disinfect the RV’s fresh water tank after the long winter storage. Even though it has been “empty,” I will be adding some bleach along with water. To fill the tank, one must use a hose. I would like to remove the disposable water filter installed by Newmar in the wet bay and add some bleach/water to the filter holder and screw it back in without the filter and flush the mixture into the freshwater tank. Will this work or is there a better way? If I left the filter in and added bleach via a hose, I suspect the activated charcoal filter would remove the bleach before it went into the tank. I am assuming the filter is between the hose fill and the tank. Your thoughts? Thanks. —Phillip, 2022 Newmar Dutch Star 4081

Dear Phillip,
Typically the city water connection is piped directly to the filter, through it, and then back to the diverter valve. This valve is turned one way to direct the water flow to the fresh water tank to fill it and turned the other way to direct pressurized water through the plumbing system. So you can remove the filter, fill the canister with bleach, and replace it to the housing. With the diverter valve directed to the fresh water tank, the pressurized water from the outside source will push the bleach into the tank.

Easiest way to sanitize a fresh water tank

The easiest way to sanitize a fresh water tank is to pour either a bleach solution or sanitizing liquid down the gravity fill; however, it does not look like your unit has that. A gravity fill is an open hole on the side that allows you to put a garden hose in and fill the tank if you do not have access to a fill hose with a threaded end. Many rest stops and dump stations had a spring-loaded potable water station with a hose that had the end cut off. If you have just the diverter valve model, you cannot fill the tank at one of these stations. Many RV manufacturers that build the larger motorcoaches figure their owners probably won’t use these stations.

Most of the units I have had over the years did not have a permanently mounted filter in the service center; rather, I purchased an in-line version. To sanitize the fresh water and the plumbing, I would fill the garden hose with a bleach solution and connect it to the city water fill, which would do the same thing.

Another option to sanitize fresh water tank

Another option would be to use this handy gadget that can be connected to the outside pressurized source and then to the supply hose going to your rig.

You will need a short supply hose that connects to the outside faucet and then the inlet of this sanitizer and your supply hose will fit the other end. This will allow you to pour in whatever amount you want. You can find it at Amazon here.

If you do not like the smell of bleach, I would recommend using the Thetford fresh water tank sanitizing product. This is a two-step process and this sanitizer would be the best option.


 You might also enjoy this from Dave 

How do I prepare a fresh water tank for use?

Dear Dave,
I have a 2018 trailer and would like to use the fresh water holding tank. I have never used it but the previous owner may have. How do I clean or prepare a holding tank for use? —Carol

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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2 months ago

In my country before I came to USA, I was taught that if it doesn’t kill you, it doesn’t kill bacteria, where as bleach always kills bacteria, therefore I always use the RV Inline Sanitizer to add and clean my fresh water supply in my motor home.

Steve Hericks
2 months ago

Activated charcoal ‘removes’ organic contaminants of which bleach is one. If you flush bleach THROUGH your activated charcoal filter, you will not disinfect it, you will destroy it. If you ever do, the only solution is to replace the filter. Charcoal filters can become inactive without being clogged with particulates (which would cause excessive back pressure) so a periodic replacement, based on how much chlorinated water is processed is needed.

2 months ago

Money Saving Tip:

The Thetford product is very expensive. At $12 to do a 24 gallon tank (you have to use an oz per gallon and the kit bottle is 24 oz) it would cost $52.50 to do the 105 gallon tank on a Dutch star.

Generic bleach costs around $3 a gallon. 1 3/4 cups required for the same tank (1/4 cup per 15 gals) or around 35¢.

I’ll take the money saved by using bleach and use it to pay for an extra night of camping or another 10 to 15 gallons of fuel in my tank!

Jim Johnson
2 months ago

Our camper has the separate gravity fill water intake. E-Z P-Z to sanitize the storage tank. But our larger trailer has only the hose connection with a diverter valve. Tough to inject bleach through there; so I like the linked garden hose tank.

However, there is typically another way… The fresh water storage tank has to have a vent, and typically it is right next to the hose connection / diverter valve. Typically it is screened with a rubber gasket holding the screen. This screen can be easily removed by popping it out with a small flat blade screwdriver at the outer edge of the retaining gasket.

I carry an angled funnel that fits into the tank vent and introduce my bleach through the vent and flush residual bleach in the vent down into the tank with a little water. Note that you must slowly pour the liquid into the vent as it also has to allow air to be expelled from the tank.

I typically put some water into the tank via the diverter before adding bleach.

2 months ago

Another way is to use a winterizing hand pump. Camco makes one. About 1/2 the price of the tank type.
Calculate the amount of bleach needed, 1/4 cup per 15 gallons, put that in a gallon container and fill with water. Pump that solution into the fresh water fill. Then fill the tank. Bypass the water heater and run all faucets until you smell bleach, then let it sit overnight. Drain the tank, refill and run all faucets again.

Neal Davis
2 months ago

Thanks, Dave!

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