Hello Hudson. And welcome
I have a 1983 h34 roughly the same vintage
By the way h37 is a great boat sailed that model a lot.
The most conventional method is to drain all the water tanks thru the hot water faucet untill all water is out. Don't forget to turn of the hot water breaker. After the tanks have run dry turn off the water pump. Ad approximately three to six gallons of consecrated none toxic antifreeze -50 degrees into the mane tanks. Turn on the water pump and let the antifreeze get pumped into the hot water tank and thru the hot water lines to the faucet, when you see antifreeze flow thru then that line is done. Note that for the first few seconds the antifreeze may be a bit diluted, let it flow untill you see the concentrate antifreeze come out. Repeat process with the shower and any other faucets. Now do the same with the cold side. Now the water system is winterized.
The winterize the sanitation system pump out the holding tank fill with fresh water and pump out Again. Flush the hold tank about three or four times to get it as clean as possible. After the holding tank has been pumped out then and two or thee gallon on -50 none toxic antifreeze thru the head. Before drying the bowl add about 1 oz. of vegetable oil to lubricant the internals of the pump.
Don't forget to do the engine.
You can also blow out all the tanks and heater using a leaf blower or shop vac but that requires you to disconnect all the water lines from the water pump after every thing has been drained thru the hot water faucets then disconnecting the in and out of the hot water heater
You then blow out all remaining water from the tanks to the pump.
Then from the pump supply lines to the faucets ant to the heater.
Blow out the heater Inline until the outlet line is dry.
Next blow out the hot water supply lines to all faucets.
This method is more labor intensive and if you don't get all of the water out of the system, you can cause damage to the tanks, heater, water lines. However if done properly with save your time in the spring flushing the none toxic antifreeze out of the water system.
If you are new and not sure what you are doing used the antifreeze conventional method it's easier and you are less likely to damage the water system.
