Knowing how to sanitize rv tanks is basically a rite of passage for anyone who spends more than a weekend living out of a trailer or motorhome. It isn't the most glamorous part of the lifestyle, but if you've ever turned on your tap after the rig has been sitting in storage for a few months and caught a whiff of something resembling a swamp, you know exactly why it's necessary.
Stagnant water is a breeding ground for all sorts of nasty stuff, including bacteria, mold, and biofilm. Even if the water looks clear, it might not be safe to brush your teeth with, let alone drink. Taking a few hours once or twice a year to clean things out ensures your fresh water stays fresh and your waste tanks don't become a biological hazard.
Getting Started With the Fresh Water Tank
The fresh water tank is your top priority because that's what you're cooking with and washing your face in. Most people use regular household bleach for this, and honestly, it's still the gold standard. It's cheap, it's effective, and it's easy to find at any grocery store.
Before you start pouring stuff in, you need to make sure your water heater is turned off. If it's electric, you could burn out the element if you drain the tank while it's on. Once that's cooled down, go ahead and drain your entire system. This includes the fresh water tank itself and your low-point drains.
Don't forget to remove any water filters. If you have an inline filter or one under the sink, the bleach will likely ruin it, and the filter itself might actually trap some of the gunk you're trying to flush out. Just bypass them or pull the cartridges out for now.
The Magic Ratio for Bleach
You can't just eyeball the bleach. Too little won't kill the bacteria, and too much will make your water smell like a public swimming pool for the next six months. The general rule of thumb is 1/4 cup of bleach for every 15 gallons of tank capacity.
If you have a 30-gallon tank, you'll need half a cup. If you're rocking a massive 60-gallon setup, you'll need a full cup.
Here's a pro tip: don't pour straight bleach directly into your gravity fill. It's better to mix the bleach into a one-gallon jug of water first. This helps it distribute better and prevents the concentrated bleach from eating away at any seals or plastic fittings it touches right away. Use a funnel, pour your mixture in, and then fill the rest of the tank with fresh water from your hose.
Circulating the Solution
Once the tank is full of your bleach-water mix, you aren't done yet. You need that sanitized water to reach every inch of your plumbing. Turn on your RV's water pump and go to every single faucet—hot and cold side.
Run the water until you can distinctly smell the bleach coming out of the tap. Do this for the kitchen sink, the bathroom vanity, the shower, and even the outdoor shower if you have one. Don't forget to flush the toilet a couple of times too. Once you smell that "clean" scent at every outlet, shut everything off.
Now comes the hard part: waiting. You need to let that mixture sit in the lines and the tank for at least three to four hours. If you really want to be thorough—or if the RV has been sitting for a year—let it sit overnight. Some people like to take the RV for a quick drive around the block during this time. The sloshing action helps the bleach water reach the very top of the tank where mold sometimes likes to hide.
Flushing the System
After the waiting period is over, it's time to get that bleach out. Drain the fresh water tank again. It's going to smell pretty strong, so try to do this somewhere where the bleach won't kill your prize-winning grass.
Refill the tank with fresh, potable water and run all the faucets again. You're looking for that bleach smell to disappear. It usually takes two or three full cycles of filling and draining to get the water back to tasting and smelling normal. If you're still catching a hint of chlorine, you can mix a half-cup of baking soda with some water, pour it in, and flush one more time. It's great for neutralizing the scent.
Dealing With the Grey and Black Tanks
While "how to sanitize rv tanks" usually refers to the fresh side, your waste tanks need some love too. These don't necessarily need to be "sanitized" in the sense that you'd drink from them, but they definitely need to be disinfected to keep odors down and sensors working.
For the black tank (the toilet one), the best thing you can do is a deep clean using a tank wand or a built-in flush system. After you've dumped the tank at a station, use a high-pressure hose to spray out the interior walls.
If you're dealing with a "poop pyramid" or sensors that always read full, try the ice cube trick. Dump a couple of bags of ice down the toilet along with some soapy water just before you hit the road. As you drive, the ice acts like a scrub brush against the walls of the tank. By the time you get to your destination, the ice has melted, and you can just dump the mess.
For the grey tank (sinks and shower), grease and soap scum are your biggest enemies. You can use a dedicated grey tank cleaner or even just a good grease-cutting dish soap like Dawn. Pour it down the drains with some hot water before a long drive, and it'll break up that sludge that causes that "sour" smell.
Alternative Sanitizing Methods
Maybe you hate the smell of bleach, or you're worried about it being too harsh on your system. There are alternatives, though they usually cost a bit more.
Hydrogen peroxide is a popular choice for people with sensitive systems. You'll need a lot more of it than bleach (usually about a quart of 3% peroxide for every 25 gallons), but it's completely odorless and breaks down into just water and oxygen.
There are also commercial RV tank sanitizers. These are usually "one-step" solutions that you just pour in, let sit, and rinse. They're great because they're formulated specifically for RV plumbing and won't dry out your rubber seals. Just follow the directions on the bottle, as the concentrations vary wildly between brands.
When Should You Do This?
Ideally, you should be looking at how to sanitize rv tanks at least twice a year. The most important time is right after you take it out of winter storage. Even if you drained it perfectly, a tiny bit of moisture left in the dark can grow things you don't want to meet.
The second time should be right before you put it away for the season, or if you've been forced to fill up your tank from a questionable water source (like a rusty well at a remote campground).
A Few Final Tips
- Check your anode rod: While you're messing with the water system, pull your water heater's anode rod. If it looks like a chewed-up piece of gum, replace it. It's cheap insurance for your water heater tank.
- Don't use scented bleach: Stick to the plain, "Original" stuff. The "Splashless" or "Outdoor" versions have additives and thickeners that you really don't want in your drinking water.
- Sanitize your hose too: It doesn't do much good to have a clean tank if your drinking water hose has been sitting in the sun with old water in it. Occasionally run a bit of the bleach mixture through the hose itself.
Keeping your water system clean isn't a fun Saturday afternoon, but it's a lot better than getting sick on your vacation. Once you get the rhythm down, the whole process only takes about 30 minutes of actual "work," with a few hours of waiting in between. Your nose (and your stomach) will definitely thank you.