Figuring out how to drain fresh water tank rv systems is one of those basic maintenance tasks that every owner needs to master sooner rather than later. Whether you're wrapping up a long weekend at the campground or getting your rig ready for the winter chill, getting that old water out is essential for keeping your plumbing in good shape. It might seem a little intimidating if you're a new owner, but once you find the right valves, it's actually a pretty straightforward process.
There are plenty of reasons why you'd want to empty things out. Maybe the water has been sitting for a few weeks and is starting to taste a bit funky, or maybe you're trying to shed some weight before hitting a steep mountain pass. Whatever the reason, doing it correctly ensures you don't damage your water pump or leave behind stagnant puddles that can grow bacteria.
Locating your drain valves
Before you can actually start the job, you have to find where the water actually exits the vehicle. Most RVs have a dedicated drain for the fresh water tank itself, along with "low point drains" for the rest of the plumbing lines.
The main tank drain is usually a single valve located on the exterior of the RV, often near where the tank is mounted. In many travel trailers, you'll see a small white or clear plastic tube sticking out from the underbelly with a simple turn-valve or a cap on the end. If you have a larger motorhome, this valve might be tucked away inside a "wet bay" or a service compartment where your hose hookups are located.
Don't confuse the main tank drain with the low point drains. Those are typically two separate lines—one for hot and one for cold—that sit at the lowest part of your entire plumbing system. While you'll want to open those eventually too, the main tank drain is what's going to handle the bulk of the 30 to 80 gallons you might be carrying.
Step-by-step: how to drain fresh water tank rv
Once you've spotted your valves, the actual process is fairly hands-off. First things first: turn off your water pump. Running a pump dry for a long period is a great way to burn it out, and you don't need it to push the water out anyway—gravity will do most of the heavy lifting.
- Open the main drain valve: Twist the handle or unscrew the cap on your fresh water tank drain. You'll probably get a pretty decent splash, so make sure you aren't standing directly under it.
- Open the indoor faucets: This is a step a lot of people skip, but it's important. By opening the kitchen and bathroom taps, you break the vacuum in the lines. It's just like putting your finger over a straw; if you don't let air in at the top, the water has a harder time coming out the bottom.
- Open the low point drains: While the main tank is glugging away, find those two low point drain lines and open them up. This ensures that any water sitting in the actual pipes of the RV gets pulled out too.
- Flush the toilet: Give the toilet a few flushes to clear out any remaining water in that specific line.
- Wait it out: Depending on the size of your tank, this can take anywhere from ten minutes to half an hour. It's a good time to go check your tire pressure or tidy up the storage bays.
Don't forget the water heater
If you're draining your system because you're done for the season, you absolutely cannot forget the water heater. It's a separate beast from the fresh water tank. Safety warning here: never, ever try to drain your water heater while the water is hot or while the heater is turned on. You'll end up with a face full of scalding steam or a burnt-out heating element.
Wait for the water to cool down completely. Then, turn off the bypass valves (if your RV has them) and unscrew the drain plug or the anode rod. The anode rod is that long metal probe attached to the plug; it's designed to corrode so your tank doesn't have to. If it looks like a chewed-up pencil, it's probably time to buy a new one anyway.
When you pull that plug, the water is going to come rushing out. Just like with the fresh tank, opening the "pressure relief valve" at the top of the heater will help it drain much faster by letting air into the tank.
Why you shouldn't leave water sitting
It's tempting to just leave the tank half-full if you know you're going out again in three weeks. However, stagnant water is an invitation for trouble. Algae and bacteria love the dark, plastic environment of an RV tank, especially if it's warm outside.
If you've ever noticed a "rotten egg" smell coming from your taps, that's usually sulfur-reducing bacteria that have set up shop in your plumbing. Draining the tank after every trip is the best way to prevent that. Plus, water is heavy! A full 50-gallon tank adds about 400 pounds to your load. That's a lot of extra weight your engine has to pull, which directly eats into your fuel mileage. Unless you're planning on "boondocking" (camping without hookups) at your next stop, it's better to travel light.
Sanitizing after a long sit
Knowing how to drain fresh water tank rv lines is only half the battle. If your rig has been sitting empty for the winter, or if you just bought a used one, you should really sanitize the system before you drink anything out of it.
The standard DIY method is using a small amount of unscented household bleach. A common ratio is about a quarter-cup of bleach for every 15 gallons of tank capacity. You mix the bleach with some water in a bucket first, pour it into your tank using a funnel, and then fill the rest of the tank with fresh water.
Run your faucets until you smell that slight "pool" scent, let it sit for about 12 hours, and then—you guessed it—drain it all out again using the steps we talked about above. Refill it with fresh water and drain it one more time to get rid of the bleach smell. It's a bit of a chore, but it ensures your water is actually safe to use for brushing your teeth or washing dishes.
Dealing with sensors
One annoying thing you might encounter after draining your tank is that your control panel still says it's "1/3 full" or even "half full." RV tank sensors are notoriously finicky. Sometimes a bit of residue or a film builds up on the sensors inside the tank, tricking them into thinking there's still water in there.
If this happens, don't panic. Usually, the tank is actually empty, and the sensor just needs a cleaning. There are sensor cleaners you can add to the tank, or sometimes just driving around with a few gallons of fresh water and some dish soap can help "scrub" the walls of the tank and reset those sensors.
Final thoughts on the process
Once the water stops dripping, go ahead and close all those valves back up. If you leave them open while the RV is in storage, you're basically inviting spiders and ants to crawl up into your plumbing system. You definitely don't want a "bug surprise" the next time you turn on your kitchen faucet.
Learning how to drain fresh water tank rv components is really just about getting to know your rig's specific layout. Every model is a little different—some have fancy electronic valves, others have simple plastic caps—but the physics remains the same. Keep it empty when you aren't using it, keep it clean when you are, and you'll have one less thing to worry about while you're out on the road enjoying the view.