How to winterize a travel trailer.

What’s in this guide

1. How a trailer differs from a cottage
2. Air, antifreeze, or both
3. Tools and materials
4. 1. Drain the holding tanks
5. 2. The water heater
6. 3. Filters, hoses and fittings
7. 4. Blowing out the lines
8. 5. The bypass, and reading the valves
9. 6. Antifreeze through the lines
10. 7. Drains, traps and toilets
11. 8. Battery and power
12. 9. Propane
13. 10. Fridge, food and moisture
14. 11. Mice
15. 12. Roof, seals, vents and slides
16. 13. Parking it for the winter
17. The printable checklist
18. The mistakes that cost the most
19. What to remember for spring
20. Common questions

How a trailer differs from a cottage

If you’ve closed a cottage, you know the principle: get the water out, put antifreeze where you can’t. A trailer follows the same principle, but almost every detail is different.

• There is no single main shutoff. Water comes in two ways: from the fresh tank through a 12-volt pump, or from a hose on the city water inlet. Both paths have to be cleared.
• There are three tanks. Fresh, grey and black. Each needs draining and each has a valve that can crack if water sits in it.
• The water heater has a bypass. Three valves (sometimes two, or one combined valve) let you route around the tank so you don’t fill it with six to ten gallons of antifreeze.
• There are low-point drains. Usually two, one hot and one cold, underneath the trailer. They are the lowest point of the supply lines and the place water settles.
• Lines run through the floor and underbelly, in spaces with little or no insulation. A trailer gets as cold as the outside air within hours.
• The fittings are plastic and the fixtures are light. That is why air pressure stays low and why a little trapped water breaks things.
• Half the job isn’t plumbing. Batteries, propane, mice, moisture and the roof cause as much spring damage as frozen lines.

Air, antifreeze, or both

There are three ways people do this:

• Air only. Blow the lines out with a compressor and stop. We don’t recommend it for an Ontario winter. Air pushes most of the water out, but what’s left keeps settling back into low spots, and droplets stay in toilet valves, faucet cartridges and water heater fittings. Those parts crack.
• Antifreeze only. Drain, bypass the heater, and pump antifreeze through every outlet until it runs pink. Sound, simple, and the method most owners use. You need a couple more jugs than with air.
• Air, then antifreeze. What we do. The air pushes nearly all the water out, so the antifreeze that follows goes in close to full strength instead of mixing with water. It uses less antifreeze and leaves nothing to chance.

Want to watch it done? These two videos are worth the time before you start: How to Winterize RV: Compressed Air & Antifreeze Method (the method this guide follows) and RV Winterizing Made Easy: Step by Step for Beginners (antifreeze only, with a tank water heater).

Tools and materials

Essential

• Keys to every exterior compartment. The water heater, pump, bypass valves, low-point drains and wet bay are often behind locked panels. One locked door means a second trip.
• Non-toxic RV antifreeze, the pink kind, in 3.78 L (one US gallon) jugs. Two to four jugs for most trailers, more for a big fifth wheel with a washer hookup. Our first trailer this fall took three, with the lines blown out first. Buy one extra.
• A way to draw antifreeze into the pump. Many trailers have a built-in winterize valve and suction hose near the water connections. If yours doesn’t, a pump winterization kit installs on the inlet side of the pump and is cheap and simple.
• A socket for the water heater plug. A Suburban (steel tank) uses an anode rod that takes a 1-1/16” socket. A Dometic or Atwood (aluminum tank) uses a plastic plug, usually 7/8” or 15/16”. Use a socket on the plastic plug, not an adjustable wrench, or you will round it off.
• Pliers and gloves, for low-point drain caps that are stiff and under pressure.
• Bucket and rags. Antifreeze goes everywhere.
• Headlamp. Everything you need is under the trailer or behind a panel.
• Phone camera, for valve positions before and after.

For the air step

• An air compressor. A portable 12-volt unit is plenty. It is pushing air through small lines, not running tools.
• A good regulator with a gauge, set to about 30 PSI before it is connected to the trailer. Not optional. Don’t count on the regulator built into the compressor: they’re made for tools, not for holding a steady 30 PSI. Ours failed on the first job. A separate inline regulator is cheap and reliable.
• A blow-out plug: a garden-hose-thread fitting with an air chuck, which screws onto the city water inlet.

Worth having

• A short length of hose and a male-to-male / female-to-female adapter, for washer connections and black tank flush inlets with awkward threads.
• A second person. One outside swapping jugs, one inside opening taps. It halves the time.
• Time. Plan on about three hours for a full air-and-antifreeze job on a travel trailer, longer the first time.
• Moisture absorbers, steel wool and expanding foam for the non-plumbing steps.

1. Drain the holding tanks

Empty all three tanks before anything else. Black first, then grey, so the grey water rinses the hose. If there is a black tank flush line, flush the black tank while it drains.

At a cottage there usually isn’t a sewer hookup, so the trailer either goes to a dump station before it is parked or the tanks are pumped out where it sits. Plan this before the trailer is parked for the season. It is much harder to arrange once it is.

The fresh tank drain is underneath, usually toward the back or near the axles. Open it, let it empty, and leave it open.

If the trailer is on a sewer connection, the tank valves can stay open while you work, and the water you push out of the lines goes straight to the sewer. Close them before the final antifreeze goes down the drains (step 7).

2. The water heater

1. Let it cool. If the heater was on, give it a couple of hours, or run a hot tap until cold water comes through; that refills the tank with cold water and cools it.
2. Relieve the pressure. Open the pressure relief valve at the top of the heater.
3. Pull the plug. On a Suburban that’s the anode rod. On a Dometic or Atwood, the plastic plug.
4. Inspect the anode. It should be one solid rod. It is designed to corrode instead of the tank, so a rod that is badly eaten away is doing its job, but it is due for replacement. Note it for spring.
5. Let it drain completely. Opening the relief valve at the top lets it drain faster.

Tankless RV water heaters hold water in a narrow heat exchanger that splits if it freezes. Most have their own drain procedure. Follow the manual for yours.

3. Filters, hoses and fittings

• Remove the water filter cartridges, inline or under-sink, and empty the housings. A filter housing is a cup of water waiting to crack. Don’t run air or antifreeze through a cartridge.
• Disconnect the city water hose, drain it and store it.
• Take off anything connected to the city water inlet and the black tank flush inlet: spray hoses, pressure regulators, filters.
• Water pump off. Then open the low-point drains and every faucet and let gravity take what it can. Close the low-point drains again before you blow out with air, or the air will just escape there.

4. Blowing out the lines

Set the regulator to about 30 PSI before you connect anything. Never go above 40. Higher pressure doesn’t clear more water; it blows apart the plastic fittings.

Start with the black tank flush

Connect the blow-out plug to the black tank flush inlet. The gauge will read close to zero, because nothing restricts that line; it goes straight into the tank. Give it five to ten seconds. It only needs a couple, but this makes sure.

Then the city water inlet, and the water heater detail

Move the blow-out plug to the city water inlet. Here is a detail most guides miss: the bypass valves often sit a foot or two from the water heater, and that stub of pipe between them stays full of water if you bypass the heater first.

1. Before bypassing, with the heater drained and its plug out, blow air in at the city inlet. This pushes water from the cold side through the heater and out the drain hole.
2. Put the plug back in temporarily and open a nearby hot tap (an outdoor shower is handy). Air now pushes the water out of the hot line between the heater and the rest of the system. Wait until it runs air.
3. Now put the heater in bypass (step 5), take the plug back out and open the relief valve. The water heater is finished.

Every fixture, hot and cold separately

• Start at the fixture farthest from the inlet, usually the kitchen. It takes longest for the air to arrive there, and once it’s clear the rest go quickly.
• Do hot and cold one at a time. Open hot, wait for steady air, close it, then do cold. That way you know each side is done.
• Expect air, then water, then air. Air pushes past the water, the water falls back and collects in a low spot, blocks the line, and the air pushes it out again. Keep going until it’s steady air. This is exactly why air alone isn’t enough.
• Shower: lay the handheld down near the drain so it doesn’t spray the bathroom.
• Toilet: hold the flush pedal down until it’s just air.
• Outside: outdoor shower, spray port, outdoor kitchen. Anything that water comes out of can freeze.
• Wet bay: if there is a tank fill or a bank of valves, flip each lever back and forth while the air is on, and leave valves at a 45° angle so neither side holds water.

Leave the washer connections, ice maker and low-point drains for the antifreeze stage. They’re awkward to blow out, and there’s only a short run of line to each.

Clear the sinks of soaps and storage and take the drain strainers out before you go further. It saves cleanup.

5. The bypass, and reading the valves

The bypass valves are usually behind the water heater: reached from inside through a cabinet, or behind an access panel. Some trailers have one combined valve, some two, most three.

In bypass, the cold supply goes straight across to the hot side without entering the tank. Skip this and you’ll pour six to ten gallons of antifreeze into the water heater before a drop reaches a tap.

6. Antifreeze through the lines

Set the pump to draw from the jug

• Built-in winterize valve: close the valve from the fresh tank to the pump, open the winterize valve, and put the suction hose in a jug. If the hose is stiff and keeps lifting out, rest something on it so it stays at the bottom.
• No built-in valve: find the water pump and fit a pump winterization kit on its inlet side. Turn the kit’s valve to draw from the jug.

Prime the system

Turn the water pump on inside and open one faucet to bleed air so the pump can prime. It takes close to a full gallon to fill the pump, lines and any filter housing. When the system is full, the pump reaches pressure (around 55 PSI on a standard pump) and shuts off on its own.

Every outlet, until it runs pure pink

• Farthest fixture first, one side at a time, hot then cold or cold then hot. Run it until it is pure pink, not pale, then close it and do the other side.
• Bathroom sink, shower, tub. Both sides each.
• Toilet: flush a few times so antifreeze goes through the whole valve, until it’s pink in the bowl.
• Outdoor shower, spray port, outdoor kitchen. Both sides.
• Washer connections, even if there is no washer installed. The lines are still there and still hold water. Screw a short hose onto each valve, run it into a bucket until clear turns to pink, then close it. What’s in the bucket is mixed with water, so don’t reuse it; pour it down a drain.
• Low-point drains: with the system under pressure, crack each cap open (pliers and gloves) until it runs pink, then close it. There are almost always two, hot and cold. Finger tight is enough; there’s a rubber gasket inside.
• City water inlet: press the check valve inside the inlet (a screwdriver or your finger) until pink comes out.
• Black tank flush line: if you can connect a short hose from the outdoor shower to the flush inlet, run some antifreeze through it. If the threads won’t mate, the air step has it covered.
• Ice maker and dishwasher: follow the manufacturer. Some can be blown out, some just need the supply line disconnected, some need antifreeze cycled through, which can take a day. If the fridge has a water filter, the ice won’t look pink even though antifreeze is getting through.

Put it back for spring

Turn the pump off. Take the hose out of the jug, close the winterize valve and reopen the valve from the fresh tank to the pump, so the trailer can be filled normally next spring. Leave the water heater in bypass; that’s undone when the tank is refilled.

7. Drains, traps and toilets

Close the tank valves first. That way some of the antifreeze you pour down the drains settles right at the valves instead of water. A grey or black valve that freezes with water in it cracks.

• Every sink: pour antifreeze down the drain to fill the P-trap. A cup or two per sink pushes out the water and leaves pink sitting in the trap.
• Shower or tub drain, the same.
• Washing machine drain, the same.
• Toilet: pour some in and flush it, so antifreeze goes into the black tank and mixes with anything left there. Then pour a little more and leave it sitting in the bowl. The seal at the bottom must stay wet; a seal left dry over winter can shrink and leak.

Outside, wipe up any antifreeze that dripped around the drains and fittings, and put any plugs and underbelly covers back on.

8. Battery and power

A dead battery is the most common thing we find in a trailer in spring. Even with everything switched off, propane detectors, stereo memory and control boards draw power, and a battery-disconnect switch doesn’t always cut all of it.

• Unplug shore power and coil the cord somewhere dry.
• Charge the battery fully, then disconnect it. A flat lead-acid battery can freeze and crack; a full one won’t.
• Better still, take it out and store it somewhere it can sit on a maintainer, or charge it once or twice over the winter.
• Lithium batteries have their own rules and most can’t be charged below freezing. Follow the manufacturer.
• Take out batteries from smoke alarms, clocks and remotes, so they don’t leak.

9. Propane

• Turn off the furnace, fridge and water heater at their controls.
• Close the valve on every cylinder.
• Cover the regulator, or the cylinders and regulator together, so ice doesn’t form in the vent and wasps don’t nest in it.
• If the cylinders come off, store them outside, upright, valves closed. Never in the trailer, a shed or the cottage.

10. Fridge, food and moisture

• Empty and clean the fridge and freezer, then prop both doors open. A closed fridge grows mould.
• Remove all food, including anything sealed. Also take out anything that can freeze and burst: drinks, canned goods, cleaning products, toiletries.
• Moisture is the slow problem. Put out moisture absorbers, leave cabinet and closet doors open, stand cushions on edge, and keep the vents cracked under covers so the air can move.
• Close the blinds. Winter sun fades fabric and dries out vinyl.
• Take home anything valuable. Trailers parked out of sight are easy targets.

11. Mice

A trailer is far easier for mice to get into than a cottage, and they do real damage: chewed wiring, nesting in the furnace ducts and insulation, and a smell that never quite leaves.

• Get underneath with a light. Every place a pipe, wire or hose goes through the floor or underbelly is a way in. Pack gaps with steel wool and seal with expanding foam.
• Check the furnace exhaust and water heater vent screens.
• No food, no crumbs, no pet food, no birdseed.
• Clean up spilled antifreeze outside.
• Set traps inside, where you’ll find them in spring.

12. Roof, seals, vents and slides

Water getting in over the winter is the expensive failure. It rots the floor and walls from the inside, and by the time you see it the damage is done.

• Inspect the roof sealant around every vent, skylight, antenna and seam. Cracks or gaps get resealed now, not in spring.
• Check the window and door seals.
• Slides: clean and condition the slide seals, then bring the slides in.
• Awning: clean, fully dry, rolled in and locked.
• Roof vents: closed, or cracked under vent covers.

13. Parking it for the winter

• Look up. Don’t park under dead limbs or a big branch over the roof. Ice and snow bring them down.
• Level it, so melt water drains off the roof instead of pooling.
• Chock the wheels and put the stabilizers down. They steady the trailer; they aren’t meant to lift it.
• Inflate the tires to the pressure on the sidewall or door sticker, and cover them against UV.
• Cover it with a breathable RV cover, not a tarp. A tarp traps moisture underneath and chafes the finish every time the wind moves it.
• Hitch lock on, and the trailer locked.
• Someone should look at it during the winter: after big snowfalls and storms, and once a month or so for signs of mice or water.

The printable checklist

Tick these off as you go. On our jobs this list is the job report, with photos at each step.

The mistakes that cost the most

• Water heater still powered while it drains. The element is gone in seconds.
• Forgetting the bypass. Six to ten gallons of antifreeze into the tank before a tap runs pink.
• Bypassing before clearing the stub to the heater. A short section of pipe full of water, right at the heater fittings.
• Air pressure too high. Over 40 PSI pops plastic fittings. Use a proper inline regulator, not the one on the compressor.
• Showing up without the keys. One locked compartment and the job isn’t finished.
• Only doing one side. Every fixture has a hot line and a cold line.
• Missing the low-point drains. They’re the lowest water in the system.
• Forgetting the outside fixtures. Outdoor showers and kitchens split first.
• Leaving a filter cartridge in. The housing cracks, and it leaks as soon as there’s water in spring.
• Washer connections with no washer. The lines are still there and still full.
• Trusting the valve sticker. Follow the pipes.
• A dry toilet seal. Leave antifreeze sitting on it.
• A flat battery left in the cold. It freezes, and it’s done.
• A tarp for a cover. Moisture underneath, scuffed finish, mould inside.
• Food left behind. Mice find it by Christmas.
• Nobody looking at it until spring. A branch through the roof in January becomes a rotted floor by May.

What to remember for spring

Things set up now that have to be undone, roughly in order:

• Anode rod or plastic plug is in the labelled bag; replace the anode if it was badly worn, and use thread tape
• Take the water heater out of bypass and fill it completely before any power or propane goes on
• Fresh tank drain and low-point drains closed before filling
• Filter cartridges back in (new ones if they’re due)
• Flush the antifreeze out of every line until the water runs clear, then sanitize the fresh water system
• Toilets and traps have antifreeze; flush and run every drain before use
• Battery charged and reconnected; alarm batteries back in
• Propane opened and appliances tested by someone qualified if anything seems off
• Roof, seals and underside inspected for winter damage before the first trip

Common questions