How to Winterize a Travel Trailer: Water System, Step by Step

The first hard freeze finds the same three parts every year: the plastic check valve inside the city water inlet, the toilet's vacuum breaker, and the clear strainer bowl under the pump. None of them holds more than a teaspoon of water. Together they cost under $60 in parts, and any one of them can put water under a floor that was never designed to get wet.

There is a towing reason to think about this before the plumbing reason. Fresh water weighs 8.34 lb per gallon, so a 40-gallon tank is 334 lb of payload, and on most trailers that tank sits forward of the axles where part of it lands on the tongue. Draining for winter is also the cheapest way to find out what your rig weighs empty.

The Short Answer

Winterizing is three jobs: get the water out, bypass the heater, then fill every line and trap with propylene glycol rated for -50°F. A 25-foot trailer with the heater bypassed takes about two gallons. The same trailer without a bypass takes nine, because a 6-gallon heater tank drinks antifreeze. Do the work before a night in the low twenties, not after the first cold morning, and do not rely on compressed air alone unless you also pour pink down every drain.

What Cracks First, and What It Costs

PEX tubing survives a freeze better than almost anything else in the system. It expands and recovers. The failures happen at the ends of the runs, in rigid plastic bodies and check valves that hold a pocket of water no drain can reach. That is why a trailer can have perfect PEX and still leak from three places in April.

Part	Why it traps water	Part cost	What it does when it splits
City water inlet check valve	A spring-loaded plunger traps a teaspoon behind the screen	$12 to $20	Cracked housing sprays inside the wall on the first pressurized hookup
Toilet vacuum breaker	Sits above the bowl, holds water after every flush	$25 to $45	Runs down the outside of the bowl and rots the floor flange
Water pump strainer bowl	Clear plastic cup under the pump, water sits below the outlet	$10 to $18	Cracks, then the pump pulls air and never builds pressure again
Water heater tank	6 gallons of water against a steel or aluminum shell	N/A	$400 to $900 for a replacement tank or whole unit
Outside shower faucet	Vertical body holds water with the handle closed	$20 to $35	Split body leaks behind the sidewall where nobody looks until spring

Part prices are typical retail for the replacement component. Repair costs assume the damage is found before the floor is wet for a season, which is the optimistic case.

The city water inlet deserves its own paragraph. Press the screen in with a fingernail and you will feel a small spring-loaded plunger. That plunger seals the line when the hose is off, and the cup behind it holds water after every trip. Blowing air through the city inlet with a blow-out plug does clear it, which is the strongest argument for owning the plug. Skip that step and the housing is the part that splits, and it splits on the inside of the wall.

Water damage is where the money goes. A split inlet leaking inside a wall cavity for a season is the same failure path described in the frame and floor inspection guide, where a soft spot in the floor turns out to be the last symptom of a leak that started a year earlier.

The Bypass, the Drains, and Two Gallons of Pink

The water heater is the single biggest line item in this job. A six-gallon tank, drained and bypassed, costs nothing to protect. Left in the circuit, it takes six gallons of antifreeze before the first faucet sees any, and that is the difference between a $10 season and a $45 one.

Trailer	Heater	Antifreeze	Cost at $5/gal
16 to 20 ft, one sink	Bypassed	1 gallon	$5
22 to 26 ft, galley and shower	Bypassed	2 gallons	$10
28 to 32 ft, two sinks and outside kitchen	Bypassed	3 gallons	$15
Same 28 ft trailer	No bypass, 6-gallon heater	9 gallons	$45

Quantities assume the fresh tank is drained rather than filled with antifreeze and that the outside shower is included. Add half a gallon for a washer-dryer prep or an ice maker line.

The two low-point drains sit under the trailer, usually behind a removable panel near the water heater or just forward of the axles. There is one for hot and one for cold, and they are the fastest way to empty the system before anything else happens. Open both, open every faucet, and let gravity do the first half of the job.

1
Drain everything first
Open the fresh tank drain, the two low-point drains, and every faucet, hot and cold. Pull the heater plug with the relief valve open. Nothing goes in until the water is out, because antifreeze poured on top of water dilutes and stops protecting.
2
Bypass the water heater
Close the two valves at the heater inlet and outlet and open the bypass valve between them, or fit the single-kit version. Confirm the bypass with a hand on the tank: it should stay cold and empty while the pump runs.
3
Push air through the lines
Fit a blow-out plug at the city water inlet, set the compressor regulator to 40 psi, and open one faucet at a time until it sputters dry. Never exceed 50 psi, and never blow through the pump with the strainer bowl removed.
4
Draw antifreeze through the pump
Attach the winterizing kit to the pump inlet, drop the hose in a jug, and run the pump until pink reaches each fixture. Work cold then hot, farthest fixture first, and finish at the toilet and the outside shower.
5
Protect what the lines do not reach
A cup of propylene glycol down each drain, a splash in the toilet bowl to keep the seal wet, and a wipe of silicone on the bowl gasket. Leave the low-point drains open, and put the heater plug somewhere you will find it in April.

One habit prevents most of the spring surprises: leave the heater plug and the anode rod in a zip bag taped inside the heater access door. An anode rod that goes missing over the winter gets replaced in June by whoever forgot it, and a heater run without one for a season is a heater with a corroded tank.

Air, Pink, or Both

The air method is faster and leaves no flushing to do in spring. It is also the method most likely to leave a pocket of water behind, because air follows the path of least resistance and a closed valve is a wall. A compressor with a small tank also pushes moisture, which is not a problem in the lines but is one more reason to follow with antifreeze.

Method	What it protects	Where it fails	Best for
Air only	Supply lines, if every low point is opened	Any water held in a trap, valve, or pump head	Mild winters, or a trailer stored where it never drops below 25°F
Antifreeze only	Every line the pump can reach	The fresh tank, if you skip it, and the heater, if you skip the bypass	Most owners, most seasons
Air, then antifreeze	Lines plus traps plus fixtures	Nothing that was opened and filled correctly	Cold climates, and any trailer stored above 5,000 ft

Air pressure at the city inlet should stay at or under 40 psi. Trailer plumbing is rated higher, but the fittings and the pump head are not rated for a shop compressor at full line pressure.

Read the jug before you buy it. The number on the label, whether it says -50 or -100, is a burst protection rating, not the temperature at which the liquid stops turning to slush. Propylene glycol at -50 strength will look like a cup of crushed ice at 0°F and that is normal. What matters is that it does not expand enough to split a fitting. Automotive antifreeze containing ethylene glycol does not belong in a trailer: it is toxic, and the taste carries into the first tank of spring water.

Spring: Sanitizing Before the First Trip

The fresh tank sat with a little water in it for five months. Even drained and stored well, the tank and the lines need a sanitizing pass before anyone drinks from them. Use plain unscented household bleach at 5.25 to 8.25 percent sodium hypochlorite. Splashless, scented, and outdoor formulas are not the same product and should not go in a potable water tank.

Tank size	Bleach	Contact time	Result
20 gallons	1/3 cup	4 hours	Roughly 50 ppm free chlorine
30 gallons	1/2 cup	4 hours	Roughly 50 ppm free chlorine
40 gallons	2/3 cup	4 hours	Roughly 50 ppm free chlorine
60 gallons	1 cup	4 hours	Roughly 50 ppm free chlorine

The ratio works out to a quarter cup of bleach per 15 gallons, which is the standard dilution most trailer manufacturers publish. Double the bleach does not sanitize twice as well; it just takes longer to rinse out.

Fill the tank, run every faucet until you smell chlorine, and let it sit. Four hours is the usual spec, overnight is common and harmless. Drain, refill, and flush until the smell is gone. A carbon filter in the galley line handles the last of the taste, and a new filter element every season is cheaper than bottling water for a summer.

Then weigh the rig before the first trip, because a full tank changes the numbers you set up the hitch around. Forty gallons is 334 lb, and if the tank sits ahead of the axles a share of that lands on the ball. On a half-ton with a thin payload margin, towing with a full tank and towing with a quarter tank are two different setups. The tongue weight calculator and the CAT scale procedure settle it in one trip; the payload calculator tells you what the water costs before you leave.

Know What the Water Weighs

A full fresh tank is payload, and part of it is tongue weight. Run your numbers before the season starts. Free, independent, no sign-up.

Water Weight Calculator Tongue Weight Calculator GVWR Calculator

Frequently Asked Questions

How much RV antifreeze do I need to winterize a travel trailer?

Two gallons covers most 20 to 26 foot trailers when the water heater is bypassed, and three gallons covers a 30 footer with two sinks, a shower, and an outside kitchen. Without a bypass, add the water heater tank: six gallons on most units, ten on some. That is the entire reason a $30 bypass kit exists. Installing one pays for itself the first season if you buy antifreeze at $5 a gallon.

Can I skip antifreeze if I blow the lines out with air?

You still need it in the drains. Compressed air clears the supply lines, but the P-traps, the toilet bowl seal, and the waste tank valves hold water that air never reaches. Pour a cup of propylene glycol into each trap and a splash into the toilet, and the air method is complete. Some owners also leave the low-point drains open all winter, which works until a valve seat dries out and drips in spring.

Can I pour antifreeze into the fresh water tank?

You can, and you will spend an hour flushing it out in spring. The tank itself drains almost completely through the low-point drain, and the small amount left has room to expand. The better method is a winterizing kit at the pump inlet, which draws antifreeze from a jug and pushes it through the lines without ever entering the fresh tank. If you do use the tank, fill it only after draining, and plan on two full rinses.

Does the water heater have to be drained?

Yes, and it has to be drained before you add antifreeze, not after. Pull the anode rod or drain plug with the pressure relief valve open so air can enter, or the tank will glug and drain slowly. Never put antifreeze in the heater tank: propylene glycol in a 6-gallon tank is 6 gallons you paid for and six gallons you have to flush out. Bypass the tank, drain it dry, and leave the plug out until spring.

When should I winterize a travel trailer?

Before the first night that stays below about 24°F for four hours. A single morning at 30°F will not split PEX, which handles short dips well because the pipe flexes. Sustained cold in the low twenties is what cracks the rigid fittings, and the forecast that matters is the overnight low, not the daytime high. If you are unsure, winterize early: the job costs about $15 in materials and an hour of your time.

Recommended Towing Safety Gear

Essential safety equipment for confident towing. We may earn a commission when you shop through these links.

RV Antifreeze, -50°F

Propylene glycol, not ethylene glycol. The -50 rating is burst protection, so the jug will look slushy at 0°F and still protect the fittings.

Check price on Amazon →

RV Water Heater Bypass Kit

Saves a six-gallon tank of antifreeze every season. Fit it once and the heater stays dry while the rest of the system gets filled.