Winterizing plumbing

Dec 2, 1997
- - LIttle Rock
Higgs' question about antifreeze vs. windshield washer fluid reminded me that it's that time of year here are the basics:


1. Drain the water tanks completely (just turn on all the faucets).

2. Drain water heater. Most have a drain petcock; follow manufacturer’s instructions to find it and use it. Remove both the inlet and outlet hoses, and if necessary use a shop vac to be sure of getting all the water out of it.

3.Do NOT put antifreeze in the water heater. Connect water heater inlet and outlet hoses together to bypass it. Bypass kits for this purpose are available from boat stores and RV supply stores.

4. Add non-toxic antifreeze ("the pink stuff") and pump that through the system until all outlets--hot and cold in the galley, head, shower, and any deck wash--run only antifreeze. Leave all the faucets open to make sure there is no pressure in the system.

As an alternative to antifreeze, some owners prefer to use an air compressor to blow all the water out of the plumbing. This does require disconnecting some fittings in low places where water can pool.


1. Pump holding tank out, then rinse thoroughly by completely filling with fresh water and 1 gallon of white vinegar twice.

2. If your toilet uses onboard pressurized water, all you need to do is flush antifreeze into the tank...winterizing the fresh water system took care of the rest.

Sea water toilet: Close toilet intake through-hull, disconnect inlet hose and stick it in a gallon of non-toxic ("the pink stuff") antifreeze. Pump the whole gallon through the system into the holding tank. Do not reconnect head intake hose to the through-hull.

3.Manual toilet: Pump the head 50 times to get as much fluid out of the system as possible.

4. After the boat comes out of the water, open all the sea cocks to drain any trapped water.

Do not use antifreeze in a Lectra/San or PuraSan. Follow manufacturers instructions to winterize all Type I and II MSDs.
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Dec 2, 2003
Hunter 410 Chester, MD (Kent Island)
Peggy, a question about the vinegar in the holding tank step

Do you put the gallon of vinegar in the toilet and pump it through to the tank, or should it be poured in the pump out hose? I want to make sure it won't harm the toilet pump, seals, etc.

Also, is there any harm or benefit in putting the gallon of vinegar into the tank , fill with water, and letting it sit in the tank all week, and then pumping it out next weekend?

Thanks for all of your help on this site! Bruce Mulford
Dec 2, 1997
- - LIttle Rock
Flush it down the toilet

I'm surprised that in the 7 years you've been here you're still not aware that a cupful of distilled white vinegar (NOT cider or any other kind) flushed all the way through the system once a week prevents mineral buildup in the head discharge hose. Don't leave it sitting in the bowl....flush it ALL the way through to the tank.

A gallon of vinegar in the tank before winterizing just "freshens" it a bit...reduces any remaining odor and also "sweetens" the hoses a little. Leaving it in the tank for a week will do no more good OR harm than pumping it out after an hour.
Nov 22, 2008
Endeavour 32 Portland, Maine
3.Do NOT put antifreeze in the water heater.
I never have, always draining and bypassing as you suggest. I'm curious though, what is the problem, aside from using a lot of anti-freeze, from putting it in the hot water heater?

My heating system radiator tank is designed so that small amounts of hot water can be drawn from it for washing up in the head when the main hot water tank isn't heated up. I didn't think to include an easy way to bypass it when I installed it. I'd like to fill that tank with the anti freeze, make sure it's well distributed through the heating system plumbing, and then drain the tank back through into the main water tank, which there is a cross over valve for. Do you see a problem with this? It will go through the usual flushing in the spring.

BTW my main water tank with the heating system cross connect is for wash water only. I have a separate potable water system.
Dec 2, 1997
- - LIttle Rock
There are a couple of problems with it

Because water comes into a water heater at the bottom and leaves at the top, it takes FOREVER to flush antifreeze out of one....even after you think you've gotten all, your coffee can still taste like antifreeze.

If you decide "to hell with it, I'll just live with the taste/smell for a while," depending on how much is left in water heater, that can cost you a heating element or damage the anode or anodizing on the inside of the tank.

It's SOOO much easier just to drain and good reason not to.


Jun 7, 2004
Freedom 38 Bristol
Re: There are a couple of problems with it


On the winterizing of the head, what do I lose by simply pumping the antifrees (pink stuff) from the bowl (with the valve on dry) rather than taking the hose from the pump and sticking it into the pink stuff.

As always, thank you.
Dec 2, 1997
- - LIttle Rock
You only winterize half the system if you do that.


On the winterizing of the head, what do I lose by simply pumping the antifrees (pink stuff) from the bowl (with the valve on dry) rather than taking the hose from the pump and sticking it into the pink stuff.
Nothing that goes into the bowl is recirculated through the intake line, pump or channel in the rim of the bowl--at least it's not supposed to! just goes through the bottom of the pump and out the toilet discharge. So if you just pour antifreeze into the bowl instead of putting the intake hose into the jug and pulling it through the toilet, you won't winterize the toilet, only the tank.

We sold a lot of bowls every spring to people who learned that the hard way.
Oct 14, 2010
Pearson P36 Rockland, ME
I've got a bit of a problem, the sea cox on my head does not close/move, boat is going to stay in the water this winter in MD, should I worry to much about this, boat has been in the water short of a one day hual for CB repair and paint, for the last ten years in FL, so she hasn't been winterized for a long time. Next year she will be on the hard in Maine and all sea cox will be removed and revitilized/replaced.
I may ;lace a small lightbulb in the locker with the hoses or should I pull the hose and cap it. the head it's self is close to shot anyway, been using a bucket.
Dec 2, 1997
- - LIttle Rock
If it were MY boat...

I'd pay the yard for a "short haul" and replace that frozen seacock NOW! 'Cuz although you've gotten away with leaving it open all the time so far, the leading cause of boats sinking in their slips is open head seacocks when no one is aboard. Then, if the toilet is headed for the dumpster anyway--so I'd guess the hoses are too--I'd add antifreeze--only the non-toxic potable kind--to the tank and call it done as far as winterizing the sanitation system is concerned.

Or maybe not quite yet...'cuz you just might wanna keep the bowl (if you're wondering why I'd suggest THAT, check this out PHII PHC LBA ) you might want to find a way to make sure there's no water in anywhere in it that can freeze, expand and crack it.


Apr 5, 2012
Hunter 31 Chesapeake Bay, MD
Two questions:

Why not reconnect the head intake hose to the seacock after it's full of antifreeze? Wouldn't doing so add a degree of preventing the boat from sinking if the seacock leaks/fails internally?

What about the sink drains? On my H31 the head sink drains above the water line, but the galley sink doesn't. Shouldn't I open the seacock, pour antifreeze into the drain and close the seacock to avoid untreated water from standing in the drain line?

Thanks, Peggy. Your book is on my Christmas list.
Jan 2, 2012
Ho'oluana 25' Reeds Bay Hawaii
This really isnt a reply...but I do have a question. I inherited a Hunter 25ft with a jabsco manuel toilet. It looks to be hooked up correct and the seacock valve is clear. I always used a porta-potty (no pump out stations here in Hilo Hawaii). I tried the pump and doesnt get any action pumping for seawater for cleaning. There isnt any pressure from the pumping and I cannot draw water up or to the holding tank. Is the pumping system shot? I tried to half fill the bowl and it emptied but will not fill...Mahalo
Feb 17, 2006
Lancer 27PS MCB Camp Pendleton KF6BL
Kamanodental, this post is several years old. You might have better luck if you start your own thread. Just cut and paste your question from above into a new thread.
Jul 5, 2011
Oday 28 Madison, CT
One thing I learned about treating my fresh water lines (pressure water) was not to put the pink stuff in the tank as it takes a lot of it (and a lot of time) to get the faucets to run "all pink". I cut a hole in the top of the tank, installed a 5" port (also helpful for cleaning the tank!) and now I empty the tank and then take a (I think 1/2") tube and push it into the tank's outlet. I put the other end into the gallon of anti freeze and turn on the pump. This brings the pink through the pump, into my 1 gal diaphragm tank and out to the faucets. Does not take long or much to get the 100% pink.
Jan 22, 2008
Beneteau 323 Annapolis MD
I'm sure some people dump GALLONS of pink into the tank before starting to pump. I pump the water out until I hear the pump "starving" for water. Then I add just once gallon at a time to the tank. When the pink starts coming out the faucets, I collect it into jugs for other use.
Sep 25, 2008
Alden 50 Sarasota, Florida
Don't know why some bother putting any antifreeze in tanks. Just empty them. What little water remains has plenty of room to expand when it freezes.
It's easy to remove the tank hose and put it in the antifreeze jug while activating the pump even if a hose extension is required.

When we lived up north, I never needed more than 2.5 gal of antifreeze to winterize 4 water tanks, 2 heads, 2 AC units, the engine and 3 showers.

Now that we live here, winterizing means putting more air in the fenders.
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Mar 26, 2011
Corsair F-24 MK I Deale, MD
a. If you leave the boat in the water and need to winterize the head, adding a tee, valve, and hose barb in the heat inlet line is very handy. First do what Peggy said, then let some of the AF drain down through the seacock before closing. Easier than taking a hose off too. In this case, you close the seacock to lock the glycol inside the valve. In Peggy's example, the valve is left open to make certain there is NOT a plug of water inside the valve to freeze. A lot of those are cracked each winter too.

b. I favor using EG (automotive antifreeze in the head. First, there is no difference in marine toxicity or in biodegradability. That is urban legend. You can check the MSDSs from confirmation. Second, I think it is very unlikely that anyone is going to drink from the black water system. The reason to do this? Many heads, including Jabsco, have neoprene joker valves and parts, and neoprene is not compatible with propylene glycol, while ethylene glycol is. You can look that up on any chemical compatibility chart. EG is simply better for the system and neutral for the head. Of course, PG should go in all potable water systems and in engines systems that interconnect with hot water heaters (never know when you might get a leak) through a heat exchanger.
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