Learning how to drain rv water tank is one of those chores that isn't exactly glamorous, but it's absolutely necessary if you want to keep your rig in good shape and your water tasting fresh. Whether you're wrapping up a weekend trip, getting ready to winterize your camper, or you just realized that the water in your tank has been sitting there since last summer (yikes), getting that old water out is the first step to a clean system. It's not a hard process, but if you've never done it before, it can be a little confusing to figure out which valve does what.
Most people think you just open a faucet and wait, but there's a bit more to it if you want to do a thorough job. You've got the fresh water tank itself, the water heater, and those pesky low-point drains that like to hide in the dark corners of your undercarriage. Let's break down exactly how to get your plumbing bone-dry without causing any headaches.
Why you should bother draining your tank
Before we dive into the "how," let's talk about the "why" for a second. If you leave water sitting in your fresh tank for weeks on end, it's going to get stale. In the worst-case scenario, you'll start growing algae or bacteria, and suddenly your morning coffee tastes like a swamp. Nobody wants that.
Another big reason is weight. Water is heavy—about 8.3 pounds per gallon. If you're hauling a 50-gallon tank full of old water, you're adding over 400 pounds to your load. That's a lot of extra work for your truck or engine for no reason. And of course, if you live somewhere where the temperature drops below freezing, leaving water in your lines or tank is a recipe for a very expensive repair bill when those pipes inevitably burst.
Finding the right valves
The first trick to how to drain rv water tank is actually finding the drain. Every RV is a little different, but most fresh water tanks have a specific drain valve located on the outside of the rig, usually directly underneath where the tank sits.
On some trailers, it's a simple white plastic petcock that you twist. On others, it might be a larger gate valve that looks like a miniature version of your black tank pull. Sometimes, it's tucked away inside a "wet bay" behind a plastic door. If you can't find it, look for a small hose poking out from the bottom of your RV's underbelly—that's usually the exit point.
Locating the low point drains
While the main tank drain gets the bulk of the water out, your pipes still hold a surprising amount of liquid. To get that out, you need to find the low point drains. These are usually two pipes (one red for hot, one blue for cold) that stick out of the bottom of the RV. They'll have caps on them or little valves inside a cabinet nearby. Opening these ensures that gravity pulls the water out of the actual plumbing lines, not just the holding tank.
Step-by-step: Draining the fresh water tank
Okay, let's get to the actual work. First, make sure your water pump is turned off. You don't want it trying to suck air once the water level gets low, as that can burn out the motor if it runs dry for too long.
- Open the main drain valve: Go ahead and twist that petcock or pull that handle. Depending on how much water you have, this could take anywhere from ten minutes to an hour. If you're at a campground, try to do this over a drain or in an area where you won't create a giant mud puddle for your neighbors.
- Open your faucets: To speed things up, go inside and open all your faucets (kitchen, bathroom, shower). This breaks the vacuum and lets air into the system, which helps the water flow out much faster. It's the same logic as putting a hole in the top of a juice can to make it pour better.
- Flush the toilet: Give the toilet a few flushes to get the remaining water out of those specific lines.
Don't forget the water heater
This is the part that a lot of people skip, and it's arguably the most important. Your water heater holds anywhere from 6 to 12 gallons of water that won't drain out through the main tank valve.
Wait! Before you touch the water heater, make absolutely sure the water is cool. If you've had the heater on recently, that water is scalding hot and under pressure. Turn it off, let it sit for a few hours, or run the hot water faucet until it comes out cold. Also, make sure you turn off the electric and gas switches to the heater so you don't burn out the heating element while the tank is empty.
How to pull the plug
Once it's cool, head outside and open the water heater access panel. You'll see a large drain plug at the bottom. Some use a plastic plug, while others (like Suburban brand heaters) have an anode rod attached to the plug. Use a socket wrench to unscrew it.
Pro tip: Open the pressure relief valve (the little silver lever at the top) before you pull the plug. If you don't, the water will come out in a sputtering mess. With the valve open, it'll flow out in a nice, steady stream.
Finishing up with the low point drains
Now that the main tank and the water heater are empty, it's time for the final step. Go back to those red and blue low point drains we found earlier. Unscrew the caps or open the valves. You'll likely see a final "whoosh" of water come out.
At this point, I usually like to turn the water pump on for about 5 to 10 seconds—no longer! This just helps push any remaining puddles out of the pump housing and into the lines to drain away. Once you see the water stop dripping, you're officially empty.
Sanitizing after you drain
Since you've already gone through the trouble of learning how to drain rv water tank, it's a great time to think about sanitizing. If your water has been sitting for a while, just draining it isn't always enough to kill off any lingering "funk."
The standard "recipe" is about 1/4 cup of unscented household bleach for every 15 gallons of tank capacity. You mix the bleach with water in a gallon jug, pour it into your fresh water gravity fill, and then top off the tank with fresh water. Run your faucets until you smell bleach, let it sit for about 12 hours, and then—you guessed it—drain the whole thing again and flush it with fresh water until the bleach smell is gone.
Common mistakes to avoid
I've seen plenty of people make simple mistakes that end up causing a mess or a broken part. One of the biggest is being too rough with the plastic drain valves. They get brittle over time due to sun exposure and road grime. If it feels stuck, don't force it with a pair of pliers, or you'll be heading to the RV supply store for a replacement. A little bit of silicone spray can go a long way.
Another mistake is forgetting to put the plugs back in. It sounds silly, but I can't tell you how many times I've started filling my tank at a campsite only to realize water is pouring out the bottom because I left the drain open from my last trip. I like to leave my valves open while the RV is in storage to let it breathe, but I always put a reminder note on my steering wheel so I remember to close them before I fill up again.
Keeping things fresh
Draining your RV water tank doesn't have to be a major chore. Once you know where the valves are and the order of operations, it's a 15-minute job that saves your plumbing and keeps your water tasting great. Plus, your engine will definitely appreciate not having to lug around all that extra weight on your next mountain climb.
So next time you're pulling back into the driveway after a great trip, take a few minutes to let that water out. Your future self—the one who doesn't have to deal with smelly water or frozen pipes—will definitely thank you. Happy camping, and stay dry!