Winter is in a holding tank.

[Impaler]

I’m new to holding tanks and now that my boat is out of the water I wonder what should be done to protect the holding tank, pump etc. I plan to flush it with fresh water (it’s got some salt water only in it just now) and then pump it out but is it a good idea to flush it through with an anti freeze with corrosion inhibitor? It might well freeze here as it’s in an open ended barn in Aberdeenshire.

Autocorrect screwed up the thread title. I don’t plan to spend winter in the tank.

 

[Boathook]

Just totally drain the holding tank and associated pipework. Antifreeze and corrosion inhibitor may affect the plastics and if put in through the toilet may cause problems with the pump seals, etc.

 

[Greenheart]

I agree, I think the title says it all, Winter is in a holding tank. The shorter days and darker evenings are a sad time.

Not quite sure I would have called the whole season a sh1t, but I'm glad someone else effectively has.

 

[thinwater]

Ethylene glycol antifreeze will not damage any of the plastic or elastomer parts. It is the blackwater systems, so no one is going to drink it. Propylene glycol can damge certain plastics and neoprene joker valves.

[I spent decades in the antifreeze industry]

A summary here.
http://sail-delmarva.blogspot.com/2009/11/marine-winterizing-antifreeze-and.html

 

[BabaYaga]

I have never used antifreeze in my tank and have never had any frost damage.
But I guess it depends on the shape of the tank and type of pump.
Mine is a self draining stainless steel tank and a manual diaphragm pump.

 

[thinwater]

The usual practice here, where it gets pleanty cold, is to pump the tank as dry as possible, and then suck about a gallon though all the way from the intake (not just in the bowl--that does not protect the inlet system). Enough ends up in the tank.

 

[BabaYaga]

It gets plenty cold here as well.

 

[thinwater]

It gets plenty cold here as well.

Yeah, I'm sure!

Burst pipes and pumps depend a lot on geometry. Some designs, the ice can shift, others it is trapped. Most folks suggest glycol because it's impossible to be sure, until after something breaks.

 

[Impaler]

Thanks all.