How do I sanitize my freshwater tank?

Sanitizing your freshwater tank – even if you rarely use it – is very important. Holding tanks are wet, warm, and exposed to molds, yeasts, bacteria, viruses, and other harmful organisms. Left unsanitized (or used), who knows what will find a home there and cause potential problems. Many respiratory aggravates can be found inside unsanitized freshwater holding tanks, especially.

Sanitizing should be done on a regular schedule:

• Full-timers should perform the process once a quarter or four times a year
• Everyone else should sanitize their freshwater tank at least twice a year (usually after they pull it out of storage and then four to five months later, like mid-summer)

Sanitizing is a relatively easy though time-consuming process. The basic concept is to introduce an antiseptic solution into your tank, circulate it through the RV’s plumbing (so you’re sanitizing that too!), allowing it to sit for a period of time, then flushing it out.

Most RVers use a weak bleach and water solution to do the sanitizing. You can also use a vinegar and water solution, though the concentration is higher.

It’s important NOT to use splashless bleach. That has a lower concentration of sodium hypochlorite, the sanitizing element needed to clean your freshwater tank. You good, old-fashioned bottom-shelf bleach, preferably unscented.

The ratio of bleach to water is important. Use 1/4 cup (2 ounces) for every 15 gallons of freshwater tank capacity. So, for a 60 gallon freshwater tank, you’ll use one cup (8 ounces) of bleach. If you’re using vinegar, double the concentration to 1/2 cup (4 ounces) for every 15 gallons of freshwater tank capacity.

How do you get the bleach into the holding tank without splashing it all over you? The best way we’ve found is to empty your RV’s water supply hose (the sanitary white or, in some cases, blue one), careful pour the appropriate amount of bleach (or vinegar) into the hose, and then attach it to your RV’s water inlet, and fill your freshwater tank. Note that you might have to switch over your supply lever to “tank fill.” Some RV’s have separate freshwater tank inlets for tank fill vs. “city water” (from your RV park’s pressurized supply).

Once the freshwater tank is full (it should start to come out the overflow pipe or outlet), turn off the fill supply. Go inside your RV, turn on your water pump, and open every tap inside (don’t forget the outdoor shower or outside kitchen sink tap, if you have them) until you smell the bleach (or vinegar) scent. You want the bleach-y (or vinegar-y) water solution to be in your RV’s plumbing pipes too!

Next is the waiting game. Common guidelines say to wait four to six hours, but we recommend leaving this solution in your freshwater tank (and RV’s plumbing pipes) overnight. After whatever period of time you decide, the next step is to get the beach (or vinegar) and water solution out of your RV’s freshwater tank and plumbing system.

Use the pump to do this. You can also open your freshwater tank’s low-point drain after the pump has been running a while if you feel the bleach (or vinegar) water will not harm the surface under your RV or run-off won’t be a problem. Be sure to keep your gray water holding tank valve open (so the freshwater tank runoff can exit into the RV park’s waste disposal or handling system).

Next, repeat the whole process (filling the freshwater tank, waiting, and emptying it) with just fresh, clean water. The wait time is the same. You can repeat this process a second time if you wish (we do for our RV, so it’s a three-day process).

What if don’t have all that time? You can double the concentration of bleach- (or vinegar) to-water and just wait two to four hours. Wait time on the tank of just fresh water (the second or even third step) should be as long as you can. With this double-concentration method, you can cut the time down to just one day for a complete sanitization.