Learning how to blow out the water lines on an RV is one of those skills that every owner eventually has to master, especially if you live somewhere where the temperature drops below freezing. It's the centerpiece of the winterization process, and honestly, it's not nearly as intimidating as it sounds once you've done it a couple of times. The goal is simple: get every single drop of water out of your pipes so that when the ground freezes, your plumbing doesn't turn into a collection of expensive ice cube trays that crack and ruin your spring.
I remember the first time I tried this. I was terrified I'd pump too much pressure into the lines and blow a fitting right off behind a wall. But as long as you have the right tools and a bit of patience, it's a very manageable DIY project. Let's walk through how to get this done without any drama.
Why blowing out the lines is often better than antifreeze
There are two main ways to winterize an RV: the "wet" method and the "dry" method. The wet method involves pumping pink RV antifreeze through the entire system. While it works, some people—myself included—aren't huge fans of the taste and smell it leaves behind in the lines for the first few trips of the following year.
By knowing how to blow out the water lines on an RV, you can opt for the dry method. This uses compressed air to physically push the water out of the faucets and drains. It keeps your fresh water system "clean" in the sense that you won't have to flush out chemical residue for three hours in April. However, keep in mind that even if you blow out the lines, you'll still need a tiny bit of antifreeze for your P-traps and waste tanks, but we'll get to that.
The gear you'll need to get started
You don't need a massive industrial setup, but you do need a few specific items. If you try to just stick an air hose against your city water inlet, you're going to have a bad time.
First, you need an air compressor. It doesn't have to be a giant tank; even a small "pancake" compressor works fine. The most important feature is that it needs a regulator so you can control the pressure.
Second, you need a blowout plug. This is a small adapter that screws into your RV's city water inlet. On one end, it has the standard hose threads; on the other, it has a quick-connect nipple for your air hose (or sometimes a Schrader valve, like on a tire). I highly recommend getting the brass version rather than the cheap plastic ones; they seal better and last forever.
Step 1: Drain your tanks and water heater
Before you ever touch the air compressor, you need to get the bulk of the water out of the system. Start by opening your fresh water tank drain and letting it go until it's empty.
Next—and this is the big one—drain your water heater. Make sure the heater is turned off and the water has cooled down so you don't scald yourself. Remove the drain plug (or the anode rod, depending on your model) and let it all pour out. While that's draining, open up your "low point drains." These are usually two pipes hanging underneath your rig with caps or valves. Opening these lets gravity do most of the heavy lifting.
Pro tip: Once the water heater is empty, flip the bypass valves. You do not want to blow air through the water heater tank. It's a waste of time and can sometimes damage the tank if you aren't careful. You want the air to bypass the heater and go straight into the hot water lines.
Step 2: Hooking up the air
Now that the system is mostly empty, it's time to hook up your blowout plug to the city water inlet. Grab your air compressor and set the regulator to about 30 to 40 PSI.
This is the "goldilocks" zone. If you go too low, you won't have enough force to push the water out of the bends in the pipes. If you go much higher than 50 PSI, you risk blowing out a plastic fitting or a seal in your plumbing. Most RV plumbing is rated for higher pressure, but cold plastic is brittle, and it's better to be safe than sorry.
Step 3: The actual blowout process
This is where the magic happens. It's a lot easier if you have a partner to help you, but you can definitely do it solo.
Go inside the RV and start with the faucet closest to the water inlet. Open the cold side first. You'll hear a lot of sputtering and hissing. Keep it open until nothing but air is coming out. Then, do the same for the hot side.
Work your way through the entire RV, one fixture at a time. Don't forget: * The kitchen sink * The bathroom sink * The shower (take the head off and let the hose hang down) * The toilet (flush it several times until no more water swirls) * The outside shower (people always forget this one, and it's usually the first thing to burst)
Step 4: Don't forget the appliances
If your RV has a washing machine, an ice maker, or a dishwasher, things get a little more complicated. These often have solenoid valves that only open when the appliance is running. You might need to run a short cycle on these machines to force the air through the internal lines. If you aren't comfortable doing this, this is one area where using a little bit of antifreeze specifically for those appliances might be a safer bet.
Step 5: Dealing with the low point drains and the pump
Go back outside while the air is still running and open those low point drains again. Even if they looked empty before, the air pressure will usually find a few more cups of water hiding in the "belly" of the plumbing.
Finally, think about your water pump. Most people forget that there's a small section of line between the fresh water tank and the pump that the air compressor can't reach because the pump acts as a one-way valve. I usually turn the pump on for about 10-20 seconds (while the lines are pressurized) just to let it "burp" out any remaining water. Just don't run it dry for too long.
Finishing up with the P-traps
Even though you've successfully figured out how to blow out the water lines on an RV, your job isn't quite done. Your pipes are dry, but your P-traps (those U-shaped pipes under the sinks) and your toilet seal still need protection.
Since the air compressor won't blow the water out of a trap, you need to pour about a cup or two of pink RV antifreeze down every drain—kitchen, bath, and shower. This displaces the water in the trap so it won't freeze and crack the plastic. Also, pour a little bit into the toilet bowl to keep the rubber seal lubricated and protected throughout the winter.
Common mistakes to avoid
One of the biggest mistakes I see is people forgetting to bypass the water heater. If you don't bypass it, you're essentially trying to pressurize a 6 or 10-gallon tank before the air ever reaches the rest of the lines. It takes forever and isn't very effective.
Another slip-up is rushing the process. If you close a faucet the second you see air, there might still be "slugs" of water sitting in a low spot in the pipe. Give it an extra ten seconds of pure air flow to be sure. It's also a good idea to go through the whole "open every faucet" cycle twice. You'd be surprised how much water migrates back to a low spot after the first pass.
Wrapping it all up
Once you've gone through every faucet and handled the P-traps, you can disconnect the compressor and remove the blowout plug. I usually leave the faucets slightly cracked open over the winter—it's an old-school habit that allows for any remaining moisture to evaporate and prevents pressure buildup if the temperature swings wildly.
Taking the time to learn how to blow out the water lines on an RV is honestly one of the best ways to protect your investment. It takes about an hour once you get the hang of it, and it saves you a massive headache (and a huge repair bill) come springtime. Plus, there's a certain peace of mind that comes with knowing your rig is tucked away and ready for the deep freeze. Now you can head inside, grab a coffee, and wait for the snow to melt.