How to Winterize an RV Water System With a Blowout Adapter
To winterize an RV water system with a blowout adapter, drain the tanks and water heater, bypass the heater, then connect the blowout adapter between your city water inlet and an air compressor set to about 30 to 40 psi. Open each faucet one at a time, hot side and cold side, until only air comes out. Finish by pouring RV antifreeze into the drain traps. Most of the time goes into draining. The air pass itself is quick.
Blowing out the lines uses no antifreeze in your fresh water plumbing, which means no pink taste in spring and less to buy each fall. The catch is that it only works if you get the steps and the pressure right.
Key Takeaways
- Keep the compressor regulator at roughly 30 to 40 psi. Higher pressure risks damaging plumbing fittings.
- Bypass and drain the water heater first, or you'll waste time pushing air into a tank you already emptied.
- Open one fixture at a time, and do both hot and cold sides.
- Match the adapter's thread gender to your inlet: threads on the outside of the port need a female (FHT) adapter.
- Air clears the lines, but drain traps still need RV antifreeze.
Blowout Method vs Antifreeze Method
There are two ways to protect RV plumbing from freezing. Many owners combine them. Here is how they compare.
| Blowout with compressed air | Pumping antifreeze through lines | |
|---|---|---|
| What you need | Air compressor, blowout adapter | Several gallons of RV antifreeze, pump converter or hand pump |
| Cost each season | Close to zero after the adapter | Antifreeze every fall |
| Spring startup | Flush once and go | Flush repeatedly to remove taste and color |
| Main risk | Water left in low spots if you rush | Diluted antifreeze if lines weren't drained first |
| Best for | Moderate winters, owners who want clean water lines | Very cold storage, owners without a compressor |
If you store your rig where temperatures stay well below freezing for weeks, consider doing a blowout first and then adding antifreeze to the traps and any spot you can't fully clear. That approach gives you clean supply lines and extra protection where water tends to sit.
What PSI Should You Use to Blow Out RV Lines?
Keep it between 30 and 40 psi. That's the range recommended by RV writer Jeff Setter in his guide to blowout pressure: below 30 psi the air may not push water out completely, and above 40 psi you start risking damage to RV plumbing.
The number that matters is the regulator output, not the tank pressure. A small pancake compressor can hold well over 100 psi in its tank, so set the regulator before you connect anything. Volume is more useful than pressure here. A larger tank lets you hold a steady flow longer, which means fewer pauses while the compressor refills.
How to Winterize With a Blowout Adapter: Step by Step
Before you start, gather the compressor, the adapter, a wrench for the water heater drain, and a jug of RV antifreeze for the traps.
1. Drain the tanks and the water heater
Dump the black and gray tanks, open the fresh tank drain, and turn off the water pump. Turn off the water heater and let it cool completely, then remove the drain plug or anode rod and open the pressure relief valve to let it drain. On Suburban heaters with an anode rod, this is a good time to inspect it. If it's badly eaten away, a replacement magnesium anode rod is easy to install before storage.
2. Bypass the water heater
Set the bypass valves so air and water skip the heater tank. Without the bypass, you'll spend most of your air filling an empty tank.
3. Open the low-point drains and remove filters
Open both low-point drains to let gravity do the first pass. Pull any inline water filter cartridge so air can reach every line.
4. Close the drains and connect the adapter
Close the low-point drains. Screw the brass blowout adapter onto the city water inlet, then plug the compressor hose into its 1/4-inch quick-connect fitting. Leave the adapter's ball valve closed for now.
5. Open one fixture and start the air
Start with the fixture farthest from the inlet. Open its cold side, then slowly open the ball valve on the adapter. Let it run until only air and mist come out, then close it and repeat on the hot side. Work your way back toward the inlet: kitchen, bathroom sink, shower, outdoor shower.
6. Clear everything else that holds water
Hold the toilet flush pedal down until it spits air. Don't forget an ice maker, washer hookup, or exterior wash station if your rig has them.
7. Open the low-point drains again and do a second pass
Briefly open the low points under air pressure to blow out water that collected there. Then run through the fixtures a second time. The second pass almost always pushes out more water than you expect.
8. Protect the drain traps
Pour a cup or two of RV antifreeze into each sink and shower drain and into the toilet bowl. Air doesn't help here, because the traps are on the waste side.
MHT vs FHT Blowout Adapter: Which One Fits?
Both adapters do the same job. The difference is thread gender, and it's the most common reason a new adapter doesn't fit.
- FHT (female hose thread): threads are inside the adapter. Use it when the port you're connecting to has threads on the outside. A typical RV city water inlet works this way, the same as the spot where you attach a drinking water hose. Choose the FHT blowout adapter with ball valve.
- MHT (male hose thread): threads are on the outside of the adapter. Use it when the fitting you're connecting to has threads on the inside, such as the female end of a hose or certain inlet designs. Choose the MHT blowout adapter.
Both use 3/4-inch garden hose thread (GHT), which is not the same as NPT pipe thread. Look at your inlet before you order. If you can see the threads from the outside, go FHT.
Brass Blowout Adapter, 3/4" FHT (Female)
Fits ports with outside threads, like a typical RV city water inlet. Solid brass, built-in ball valve, 1/4" quick-connect.
$28.00
BUY NOW
Brass Blowout Adapter, 3/4" MHT (Male)
Fits fittings with inside threads, such as a female hose end. Solid brass, built-in ball valve, 1/4" quick-connect.
$28.00
BUY NOWCommon Winterizing Mistakes
- Turning the compressor regulator too high. More pressure doesn't clear lines faster. It only stresses fittings.
- Skipping the water heater bypass. You'll waste air and may still leave water in connecting lines.
- Doing only one pass. Water settles back into low spots after the first round.
- Forgetting the outdoor shower. Its hoses and valve sit outside the heated envelope and freeze first.
- Leaving the filter cartridge in place. It holds water and blocks airflow.
- Mixing up thread types. GHT and NPT fittings don't interchange.
Plumbing isn't the only thing that suffers during months in storage. Tires lose pressure and develop flat spots too. Read what happens in RV storage and your tires before you park for the season.
FAQ
Can I winterize an RV with only air and no antifreeze?
You can clear the supply lines with air alone, but the drain traps still hold water that sits outside the supply system. Pour RV antifreeze into each trap and the toilet. In very cold storage areas, many owners add antifreeze to the lines as backup.
What size air compressor do I need to blow out RV lines?
A small pancake or hot dog compressor is enough, because you only need about 30 to 40 psi at the regulator. A bigger tank simply means fewer pauses while the compressor refills between fixtures.
Why does a blowout adapter have a ball valve?
The ball valve lets you start and stop airflow at the inlet without unplugging the compressor hose each time. That makes it easier to move between fixtures and to feather the flow if a line sputters.
How do I know the lines are fully clear?
A faucet is clear when it releases only air or a light mist for several seconds. Do a second full pass after reopening the low-point drains. If water still appears on the second pass, repeat until it stops.
Finish the Job in One Afternoon
A blowout adapter turns RV winterization into a repeatable routine: drain, bypass, blow out at a safe pressure, and protect the traps. Get the thread type right and keep the regulator in range, and spring startup is just a quick flush.
Get ready before the first freeze. Pick the FHT or MHT solid brass blowout adapter for your inlet, or browse our RV plumbing and water system parts.