Saturday, September 30, 2023


Know Your RV: Sanitize your ‘new’ used RV fresh water tank

In the market for a used RV? That’s how many get into the RV lifestyle. Careful shopping can yield a pre-owned RV for far less than the price of a new rig. In many cases, “new” rigs come with factory-equipped glitches that can take forever to get rid of. Buy used and, hopefully, those problems have been fixed. A thorough inspection is always in order before you buy, but even if you hire the inspection out to a pro, there’s likely one thing you’ll never see: the inside of the fresh water tank. We highly recommend you sanitize your new rig’s tank and fresh water lines!

“Past pull date”

The reason for the sanitize project is because you’ll have no idea how long water has stood in the tank. Old water can prove to be a great place to produce some nasty odors—or worse, a bacteria colony. The same is true for “fresh” water lines throughout the rig. They might be called “past pull date” water lines.

Here’s the 11 point method to sanitize your fresh water system. These instructions are for using IF your RV has a fresh water tank equipped with a simple “pour in the water” port. Some RVs require you to hook up a water hose to a specific fitting, then flip a lever or two to fill the fresh water tank. We’ll come to that kind of system in a minute.

11 steps to sanitize that tank

1. Determine how many gallons your fresh water tank holds. Don’t have the information? If you can visually see the fresh water tank, measure it. Multiply the length, width, and depth in inches to determine the cubic inch volume. Divide that number by 231 to convert to gallons.

2. Make sure your water heater is OFF. Drain the fresh water tank completely. You’ll usually find the fresh water tank drain in close proximity to the fresh water tank. Check your owner’s manual. Drain, too, your RV gray water tank, or hook it up to a sewer system and leave the drain valve open.


3. For every 10 gallons the tank holds, put in 1 tablespoon of liquid dish detergent.

4. Fill the tank with fresh water.

5. Turn on your RV water pump, and open every water faucet and shower valve. Run the soap solution through these lines until you’ve pumped the fresh water tank empty.

6. Refill the fresh water tank.

7. Repeat step 5 until the fresh water tank is empty.

8. Mix a chlorine bleach solution to sanitize with. That’s an ounce of bleach for every 8 gallons of tank capacity. You’ll need to dilute the bleach in a gallon of water before carefully funneling it into the tank fill port. Completely fill the fresh water tank, and ensure your gray water tank is empty, or hooked up to a city sewer.

sanitize9. Open every water faucet and shower valves individually. Run the bleach solution through until you smell chlorine at the plumbing valve. Every hour, repeat the process until you IMMEDIATELY smell chlorine when you open the valve. This could take a few hours!

10. When you smell the chlorine immediately, then empty the tank by opening all the valves and running the fresh water tank empty.

11. Hate the smell or taste of chlorine? Some swear by thoroughly dissolving baking soda in water, and adding it to the fresh tank and pumping it though. It might be easier to simply make a last pass, fill the fresh tank, and pump the whole thing out through the plumbing fixtures.

Can’t just dump it in? Here’s help

And what about those who don’t have a city water inlet that allows for “dumping” liquids in the fresh tank? There are two approaches that you may try. Some of these systems have a special connection where plumbing system antifreeze can be introduced into the fresh water tank. It usually requires connecting a hose to a connection on the “water control” panel and setting the appropriate valves.

In that case you can pump any of the solutions out of a bucket and into the tank. Dilute the soap solution in a gallon of water, like you would for the bleach. When the bucket is empty, switch the hose hookup to fill the fresh tank.

Another option is to start with a dry water hose. Hook the RV end of the hose to your rig, then using a funnel (and a great deal of patience) pour the soap or bleach solution into the free end of the water hose. Now hook the hose up to the fresh water tap and pump the tank full.

How often do you need to sanitize your fresh water tank?

If you use a safe city water supply, or known “good” private well system, it’s doubtful that you’ll ever need to sanitize the system. If you’re not actively using your rig, empty the fresh tank and leave it that way until your next outing.

Some people can be confirmed germophobes, and may sanitize their system on a regular basis. If you are ever concerned that your tank may be compromised, after this initial sanitize procedure, proceed with the bleach solution—skip the soap solution.

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Finally, contrary to information that you may find on the internet, baking soda solution WILL NOT adequately and safely sanitize a fresh water system. We’ve seen others pontificate about using hydrogen peroxide for the procedure. It will sanitize, according to health experts. The CDC says, “Commercially available 3% hydrogen peroxide is a stable and effective disinfectant when used on inanimate surfaces.” But diluting the stuff will diminish or wipe out its effectiveness. Buying enough hydrogen peroxide to use full strength would seem a bit much on the finances.

Tune in next week for more “Know Your RV” tips. And if there’s something about your RV that you’d like to know, drop us a line. Use the form below, and insert “Know Your RV” on the subject line.

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Other stories by Russ and Tiña De Maris


Russ and Tiña De Maris
Russ and Tiña De Maris
Russ and Tiña went from childhood tent camping to RVing in the 1980s when the ground got too hard. They've been tutored in the ways of RVing (and RV repair) by a series of rigs, from truck campers, to a fifth-wheel, and several travel trailers. In addition to writing scores of articles on RVing topics, they've also taught college classes for folks new to RVing. They authored the book, RV Boondocking Basics.


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1 year ago

Twice a season.

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