Empty water heater, and drain pressure tank until no more water comes out. You should blow the water lines out with an
air compressor. There will be dips in your water lines that will hold water if you don't. Pour the antifreeze in all drains with
p-traps, including floor drains. Pour some in your dishwasher. Empty your toilet bowls and tanks with a shop vac and then
pour the antifreeze in both.. Also do like RS suggested and take off the shower heads. If your electric goes out for a while
and its freezing cold you will have nothing to worry about if you winterize it properly. PS. Don't forget about the ice maker.
The guys winterize a couple of dozen buildings every fall. Most of what you listed is right on the target.
We have installed tees and pressure gauges just before the inlet of the water heater, which have a ball valve, and air fitting. We turn off the water heater, and tag it out with a tag saying “refill and run water from the hot water tap in the furthest tap, before turning on water heater., and then hook the air compressor to the air chuck, and set the regulactor to about five psi lower than what the gauge was reading.
We hook a hose to the drain on the water heater, and blow out the air compressor, and the water heater becomes a secondary air chamber for the compressor. The extra volume of air lets you do a better job of blowing out the system. Let the compressor run until it recharges and shuts off.
And, then open and drain the hot water to the furthest run from the water heater, and then blow out the cold. Work your way back to the water heater, stopping if he compressor restarts to let it recharge. Then go back to the first one you did and redo them all. Yes it takes longer, but is nothing compared to the time required to redo split pipes. Particularly if they are buried in the wall. Be sure to run the washing machine and dishwasher, etc. Some of the newer ones are a real pain because they sense there is no water in teh line and don’t wan to open the valve. We made a reservoir out of some 6-inch PVC which holds a gallon of RV antifreeze, and hook it inline with the washer inlets. This flushes the antifreeze through the entire washer, including the drain pump.
Once we finish the water lines, we use the compressor to blow out the traps, using a wet rag to seal around the air gun nozzle, and then pour about a quart of RV antifreeze into them. When you do toilets pour the RV antifreeze into the over flow. That gets it into and flushes out the internal passages.
It has been about ten years since we had problems opening in the spring.