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Adding fresh water valves/drains to make winterizing easier?

Apr 19, 2020
Catalina 310 Kenosha, WI
I have a C310 that the previous owner didn't winterize that caused a number of component failures which I'm in the process of replacing (water pump, filter, lavatory valves, etc). While doing this, I see the difficulties an owner would have in doing this properly (at least by comparison to what I have in my camping trailer). I'm new to boating but am going to propose a plan that I'd like comments/feedback on so I get this right.

In particular each winter you need to:
  • empty the fresh water tank
  • empty water heater (if you have one)

Then drain or flush rv antifreeze through the following:
  • the supply lines to the pump
  • the filter and pump itself
  • the lines going to the water heater (if you have one)
  • the lines going to the sink facuets (galley and head)
  • any shower facets and heads (in the head and swim deck)
  • all sink drains
  • the head and hand pump

From experience in RV's it's easier to flush RV anti-freeze through the system then it is to use compressed air or attempt to drain everything completely. However, to do that, you need a few valves installed to make this easy to do. That includes:
  • A shutoff valve between the fresh water tank and the pump/filter intake
  • Another valve added between the pump/filter intake and a short hose that will help drain the fresh water tank and then be inserted into the jug of antifreeze that the pump will draw from when flushing the system.
  • Another shutoff valve between the pump and the hot water heater intake (this is so you can avoid filling the hot water heater with antifreeze to save $$)
If others agree with this approach and have done this, what valves did you order that you found to be a good economical choice that used the 1/2" hose barb fittings that i believe are common on boats?

thanks for advise and feedback on this.


Feb 5, 2004
Tartan 3800 Westport, MA
I know valves would make this a lot easier, but it can all be done without valves. The only valve involved in my system is a ball cock I installed to isolate the accumulator tank (which you didn't mention).

Here's what I do:

  1. shut off pressure pump;
  2. disconnect water tanks from manifold and drain into bilge;
  3. open water heater drain petcock (accumulator drains at this point, too);
  4. disconnect water heater in/out and bypass with an addition piece of tubing and connectors (this piece is stored nearby);
  5. close accumulator ballcock;
  6. disconnect input line to pump and attach temp pickup tube (this piece is stored nearby) and dip into 1 Gal. pink stuff;
  7. turn on pressure pump;
  8. once pressure is built up (pump switches off), open all taps one at a time until pink flows.
I then disconnect the head seawater inlet hose from its seacock and drop it into a gallon of pink and pump the whole gallon through. Dump 1 or 2 gallons pink into the bilge and sump and pump through; then remove strainer housings. Disconnect engine raw water inlet from its through hull and dip it into a gallon of pink and run engine enough to pump it through.

I measure the specific gravity of the pink flowing out to make sure it has sufficient freeze protection using an optical refractometer.

I think that's it.
Jul 1, 2010
Seaward 25, Catalina 350 Erie, Pa
Not sure of the details of the system on a 310, but on our 350, we have 2 water tanks, one under the v-birth and one under the aft cabin bed. The water heater has 1/2" npt threaded fittings on it, so I adapted flexible stainless lines found at the building supply store to the incoming and outgoing ends of the water lines to the water heater. For winterizing, I unscrew the lines and hook them together with a 1/2" npt nipple. This bypasses the water heater. After draining the tanks, I run a couple of gallons of -50 antifreeze through from each tank. Doesn't take very long to winterize it this way. For the water heater, I just drain it and blow out any remaining water with a shop vac.

I would prefer to put a t and ball valve in the line at each tank so I could feed the antifreeze directly into the lines instead of the tank to make recommissioning in the spring easier. Access to both tanks is a real pain, so it's just easier to just dump it into the tank fills and deal with the flushing in the spring.

Concerning the head...On ours, I added in line inlet strainer attached in the sea water line at it's highest point. I believe it's a Jabsco inlet strainer. I got a second cover for the strainer that I drilled a hole in and attached a hose nipple to. When winterizing, I remove the cover on the strainer and replace it with my custom one. I can then attach a hose and funnel to the strainer cover, and run antifreeze through the head (with the thru hull closed). Having a strainer also makes it easy to add thru hull lubricant to the other side in the spring to lube up the thru hull before launch.
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