Geoff Schultz wrote:
1) According to the boat yard, they disconnect the cold/in and hot/out
lines to the hot water heater and hook them together. Then they simply
drain the hot water tank. I did this, but I can never get all of the water
out. That makes me concerned, so I fed some anti-freeze into the tank
which will get diluted with the remaining water. Is this OK and/or how do
others winterize their hot water heater?

I avoid the "pink stuff" in the drinking water system. Do you really
want to be drinking antifreeze in the spring?

I have a small air compressor (40-50 PSI max) that I use to blow out the
lines. I start by draining the tanks as much as I can. Then I clear the
lines by opening one faucet at a time and blowing air from the just
downstream of the pump. Then I break the system at a low point in the
middle and blow from there. I can blow some extra water out of the hot
water tank, bu a small amount of water left in the main tank or hot
water heater will not be a issue.

No problems in 18 Boston winters.