Before the first real freeze of the season hits, blowing out rv water lines is one of those chores you really shouldn't put off. If you've ever dealt with a burst pipe in a house, you know it's a nightmare, but in an RV, it can be even worse because the plumbing is tucked into tight corners and behind cabinets that aren't exactly easy to reach.
The whole idea here is pretty simple: you're using pressurized air to push every last drop of water out of your pipes so there's nothing left to freeze and expand. While some people prefer to just pump the pink RV antifreeze through the whole system, many of us swear by the blowout method because it's cleaner and you don't have to spend forever rinsing that "chemical taste" out of your faucets come springtime.
What you're going to need
You don't need a massive shop-grade setup to get this done, but you do need a few specific things. First off, you'll need an air compressor. It doesn't have to be a giant tank, but it needs to be able to maintain a steady flow of air.
The most important piece of the puzzle, though, is the blowout plug. This is a tiny, inexpensive adapter that screws into your city water inlet. One side has a garden hose thread, and the other side has a tire valve (Schrader valve) or a quick-connect fitting for your air hose.
I'd also highly recommend using a pressure regulator. Most RV plumbing isn't designed to handle high pressure, and if you accidentally blast 100 PSI into your lines, you're going to be fixing leaks instead of preventing them.
Getting the system ready
Before you even think about touching the air compressor, you've got to get the bulk of the water out of the system. Start by turning off your water pump and your water heater. Whatever you do, don't forget to turn off the water heater. If you drain it while the heating element is still on (either electric or propane), you'll burn it out in minutes.
Once everything is off and the water has cooled down, go ahead and open up your low-point drains. You'll usually find these sticking out underneath your rig. Open up all the faucets inside to help the water gravity-drain out.
Next, head to your water heater. Remove the drain plug or the anode rod (usually requires a 1 1/16" socket) and let that tank empty out. Be careful here—even if the water is just warm, there could be some pressure built up, so stand to the side when you pull that plug.
The water heater bypass
This is a step that trips up a lot of people. Most modern RVs have a bypass valve for the water heater. You want to flip this to the "bypass" position before you start blowing out rv water lines.
Why? Because a water heater tank is basically a giant 6 or 10-gallon void. If you try to blow air through the whole system with the tank in-line, you're just going to be wasting your time trying to pressurize that big tank before any air reaches the actual faucets. By bypassing it, you're creating a closed loop of just the small pipes, which makes the air much more effective at clearing out the water.
Setting the right pressure
This is the part where you need to be careful. Most RV pros suggest keeping your air compressor set between 20 and 30 PSI. You might be tempted to crank it up to 50 or 60 to get the job done faster, but the plastic fittings and PEX lines in an RV can be finicky.
I usually set my compressor's regulator to 25 PSI just to be safe. It's enough force to move the water, but not enough to blow a seal on your toilet valve or a connection behind the shower.
The step-by-step blowout
Now that you're hooked up and the pressure is set, it's time to get to work. Attach your air hose to the blowout plug on the city water inlet. You'll start hearing a little bit of air moving through the lines.
Go inside and start with the faucet that is closest to the water inlet. Open the cold side first. You'll hear a lot of sputtering and see a mist of water spray out. Keep it open until nothing but air is coming out. Then do the same for the hot side.
Repeat this process for every single faucet in the rig: * Kitchen sink * Bathroom sink * Shower (don't forget to let the showerhead drain!) * Toilet (flush it until only air comes out)
Don't forget the outside shower or the spray port if you have one. These are the most common spots for freeze damage because they're essentially sitting outside the insulated envelope of the RV.
Thinking about the "hidden" water
One thing I've learned the hard way is that water hides in the weirdest places. Even after you think you're done blowing out rv water lines, it's a good idea to go through the faucets one more time. Sometimes water settles in a low spot in the PEX, and a second blast of air will catch what the first one missed.
If you have a washing machine or an icemaker in your fridge, these require a little extra attention. For icemakers, you usually have to cycle the solenoid manually to get the water out of the small line leading to the freezer. For washing machines, you'll need to run a short cycle to let the air push through the internal valves.
Don't forget the traps
Once the lines are clear, you're not quite finished. The air compressor only clears the supply lines (the pipes that bring water to the tap). It does nothing for the drain lines or the P-traps.
Every sink and shower has a P-trap—that U-shaped pipe underneath—that holds a bit of water to keep sewer smells from coming up. If that water freezes, it'll crack the plastic. Pour about a cup or two of the pink RV antifreeze down every drain to displace the water in the traps. I also like to leave a little bit of antifreeze sitting on top of the toilet seal to keep the rubber from drying out and cracking over the winter.
Air vs. Antifreeze: The big debate
You'll hear people argue about this until they're blue in the face. Some people don't trust air alone and will blow out the lines and then pump antifreeze through them. Is it overkill? Maybe. But if you live in a place where it stays below zero for weeks at a time, that extra peace of mind is worth the ten bucks for a couple of jugs of the pink stuff.
Personally, I find that blowing out rv water lines is sufficient for most climates, as long as you're thorough. The main benefit is that your "de-winterizing" process in the spring takes about five minutes—you just hook up to water and go. No sudsy, weird-smelling water for the first three trips of the year.
Wrapping it up
Once you've gone through all the steps, disconnect your air hose and remove the blowout plug. I usually leave my faucets slightly open over the winter to allow for any remaining moisture to evaporate, though some people prefer to close them to keep bugs out.
It feels like a lot of steps the first time you do it, but once you get the rhythm down, you can finish the whole process in about 30 minutes. It's a small price to pay to ensure that your first trip in the spring doesn't start with a flooded floor and a call to a mobile mechanic. Just take your time, keep that pressure low, and make sure you hit every single faucet, and your RV will be just fine until the sun comes back out.