This is the procedure I use for winterizing WindSong (stored on the hard for the winter):
Fresh Water system - I do this part with a cold engine / cold water heater:
1. Pump out all water from forward & aft tanks as close to empty as possible.
2. At the water heater, remove the cold water feed line. Using a low pressure pump (a $20 12v inflater pump), blow out the water in the tank (open a hot water faucet in one of the sinks) until sputters. This doesn't have to be completely empty, don't worry about a small amount of water that remains.
3. Remove the hot water line from the water tank and connect to the cold water feed (from number 2). you'll need 2 right angle whale fittings and about a 4-inch long piece of whale 15mm tubing to do this. Do not remove the cold water over pressure return line.
4. Add 1-2 gal of "pink stuff" to each forward & aft tank & repressurize the system from the fwd tank until pink stuff flows from the galley faucet hot & cold taps. Switch to aft tank and re-pressurize; operate each faucet, hot and cold' galley, head(s), and stern shower until pink stuff flows. Add more to aft tank if necessary.
5. Shut off the pressure pump & relieve pressure at one faucet.
At this point, the hot water heater is empty, and the water tanks, all water lines, and all sing drains have pink stuff and no water in them.
Air Conditioner:
1. Close the raw water thru-hull.
2. Connect 3-ft hose to the raw water pump, free end in gallon of "pink stuff" (you may have to prime this line to get the pump to draw fluid)
3. Run the ac until the gallon is drained, or until your partner sees pink running out the discharge line
4. Reconnect the original line to the thru-hull, but leave it closed for now.
Holding tank:
1. Motor over to the pump-out station. At the pump out station, thoroughly clean-out the holding tank. Rinse a few times with fresh water. from a hose, not the boat's water system (already winterized), through the toilet, and directly into the pump-out cap. Repeat this until the effluent is clear
2. Pour about 1/2 gal of pink stuff into the holding tank via the head (not directly into the tank).
3. While you're out motoring around - fill the fuel tank (at least 3/4) and add your favorite fuel treatment "snake-oil"
Engine:
1. Run until warm (I usually motor over to the pump-out station and back, cleaning out the holding tank while I'm there)
2. Change the oil and oil filter while the engine is still "hot".
3. Thoroughly clean and reassemble the raw water strainer
4. Shut off the raw water valve on the saildrive (equiv of a thru hull) and leave it closed
5. Disconnect the hose connecting the strainer to the raw water valve at the strainer - temporarily install a 3-ft lenght of cooling water hose (or garden hose) to the strainer
6. Fill bucket with 2-gal of "Purple Stuff" and place the garden hose free end in the bucket
7. Run engine until the bucket is drained - then shut off normally. Running the engine after the oil change will distribute the fresh oil
8. Reconnect original line from raw water inlet to the strainer but do not open the raw water valve, yet.
Shower sump:
Fill the sump with pink stuff & run pump dry. Repeat 3 times.
Bilge:
I don't winterize this if the bilge pump has not run. But you can add pink stuff to the bilge and pump it out using the electric and manual pumps, in sequence.
Haul & Block the boat - then drain the through-hull fittings:
After hauling and blocking systematically open each thru-hull, engine raw water on the saildrive, and the holding tank overboard dump while a partner collects the small amount of liquid the flows - dispose of properly. All thru-hull valves are left open for the winter. The boat has been winterized! Fuel filters and impeller pumps are serviced in the spring.