How to winterize an RV: choosing between compressed air and antifreeze without guessing wrong

It's late October and the forecast just flipped to a hard freeze overnight. You're standing at the city water inlet with a jug of pink antifreeze in one hand and a spare air compressor fitting in the other. Both work. Neither choice is wrong. What decides it is where your low points sit, how much pink taste in the spring lines you can live with, and one step almost everyone skips that quietly decides how many gallons of antifreeze you end up buying.

This is the whole job in miniature: get every trace of water out of a system that will sit below freezing for months, without cracking a fitting, splitting a low-point drain, or leaving a pocket of water in a spot neither method reliably reaches on its own.

Air or antifreeze: what the decision actually hinges on

Compressed air pushes standing water out of the lines using pressure alone. Antifreeze physically occupies the lines, so anything that's still liquid inside them is protected even if a pocket didn't fully drain. Neither claim is close to controversial among techs who do this every fall. What separates a clean winterization from a spring repair bill is whether the method matches the plumbing layout in front of you.

A single-axle travel trailer with a simple, mostly-straight run of PEX and two low-point drains is a good air-blowout candidate: a compressor and a blowout plug clear it completely. A fifth wheel with a looping bathroom bay, an ice maker line, a washer hookup, and a low point that sags below the frame rail in one spot is a different animal. Air finds the path of least resistance and can leave a sag point wet while the rest of the line reads bone dry. Antifreeze doesn't care about the sag; it fills the whole run, low spots included.

Taste is the other half of the tradeoff. Antifreeze means running every faucet in the spring until the fluid clears, and city water at the campground will carry a faint sweetness for the first few gallons no matter how thorough that flush is. Air-blown lines have nothing to flush, because nothing but air went through them. If you hate the pink-water spring ritual and your rig's low points are simple, air wins on convenience. If your layout has sags, loops, or an ice maker you'd rather not gamble on, antifreeze wins on coverage.

The compressed-air blowout method, step by step

Start by fully draining the tanks and lines, well beyond just running the faucets dry. Open the low-point drains (usually a pair of small valves under the belly, one for hot and one for cold), open every interior faucet including the shower, and let gravity finish what the pump already started. Run the pump briefly with the faucets open to clear the last of what's in the pump housing, then shut the pump off and its breaker.

Thread a blowout plug into the city water inlet and connect an air compressor. Set the regulator to no more than 35-40 psi, and start lower if a fitting looks old. RV plumbing isn't built for shop-air pressures, and pushing much higher risks popping a fitting loose. Open one faucet at a time, cold side first, and hold air on the line in short bursts until only air is coming out. Work through every faucet, the shower, the toilet valve, the outside shower if the rig has one, and the washer hookup if it's plumbed in. Leave the low-point drains open and cycle air through those lines too.

The water heater gets special handling here, and it's covered fully in the bypass section below, because whether you drain it or bypass it changes the rest of the sequence. For fixture-by-fixture cycling and compressor connections, see the full air blowout walkthrough.

Filling with antifreeze, and why the bypass step controls your bill

Antifreeze winterizing starts the same way air does: drain everything you can by gravity first. Antifreeze is meant to fill what gravity leaves behind, so the more thorough the initial drain, the less antifreeze you burn through later. From there, most rigs use a hand pump or an inline pump conversion kit that draws antifreeze straight from the jug through the fresh water pump's inlet, pushing it out through every faucet until pink fluid runs steady at each one. This is also the whole method for anyone winterizing without an air compressor at all, since antifreeze needs only a hand pump and the jugs, no shop air.

Here's the step that decides your cost far more than anything else in the process: bypassing the water heater. A water heater bypass kit is a set of valves, usually three, that reroute the antifreeze so it never enters the tank. A water heater tank typically holds 6 or 10 gallons, so bypassing it saves 6 to 10 gallons of antifreeze that would otherwise be poured out in spring. The lines themselves take only a few gallons on most trailers, more on a long rig with two bathrooms, so buy a spare jug rather than come up short. When draining the water heater before bypassing, keep in mind that on a Suburban water heater the drain plug is also the anode rod, while Atwood and Dometic heaters use aluminum tanks with a plain drain plug and no rod; see our guide on checking the anode rod. The valves themselves and the mechanics of setting them are covered in full in our water heater bypass walkthrough, since the exact valve arrangement varies enough between brands to deserve its own explanation.

Never substitute automotive antifreeze for RV antifreeze. RV and marine antifreeze is a propylene glycol formula, non-toxic and rated safe for potable water systems. Automotive antifreeze is ethylene glycol, a genuine poison that never goes in a potable system, and it affects the central nervous system, heart, and kidneys as the body metabolizes it. Green, orange, or yellow jugs from the auto parts aisle have no business anywhere near a water system a person drinks or brushes their teeth from. Only pink, RV-labeled antifreeze belongs in the fresh water side.

The low points that get skipped

Most spring repair calls trace back to the same handful of spots. The water heater bypass valve itself, if it's there but never actually turned to the bypass position. The outside shower line, which sits at the far end of the plumbing run and is easy to forget entirely. Any accumulator tank or water filter housing, both of which hold standing water that a quick air blast or a half-hearted antifreeze fill can leave behind without deliberate attention. The ice maker line on rigs that have one, since it's usually a thin tube tapped off a fitting most owners never think to trace. And the toilet valve, which needs several seconds of air or a dedicated antifreeze pour to actually clear the valve seal.

A written checklist catches what memory tends to drop on a rig this size. A rig with a full water system layout that includes tanks, pump, filter, and heater in one connected path is easier to walk methodically if you're working from a diagram; our water system overview lays out where each of those components sits relative to the others, which helps when you're deciding what still needs attention after the main lines are done.

Deciding which method fits your rig

Plenty of experienced owners run both: air first to clear the bulk of the water fast, then a modest antifreeze fill afterward to sit in the low points as backup insurance. That combination costs a little more time than either method alone, but it closes the gap each method leaves on its own.

Faucets, the fresh tank, and tankless heaters

After an air blowout, leave the low-point drains and faucets open so nothing stays trapped under pressure; after an antifreeze fill, close the faucets once pink fluid has run at each one, so the antifreeze stays in the lines and traps.

Do not fill the fresh tank with antifreeze: drain it instead, since a tank full of antifreeze takes far more product and a much longer flush in spring; a pump conversion kit or hand pump draws antifreeze straight from the jug.

Tankless water heaters do not use the bypass kit the same way and have their own drain and winterize steps in the manufacturer's manual, so follow that manual for the heater itself.

What doesn't need winterizing the same way

Holding tanks and the toilet get their own antifreeze treatment separate from the fresh water side, since a black or grey tank simply holds standing liquid in a sealed compartment. That process, along with how much antifreeze belongs in each tank, is covered in our walkthrough on winterizing the holding tanks and toilet.

If you plan to stay in the rig through freezing weather, that is a different job; see our advice on keeping water flowing while winter camping.

When spring comes

Reversing this process, flushing the antifreeze completely, resetting the bypass valves to normal operation, and sanitizing the fresh tank before you drink from it again, is its own sequence with its own failure points. That full reversal is covered in our de-winterizing walkthrough, which picks up exactly where this one leaves off.