I can't take credit for this sage advice, it comes from a fella by the handle of "Lazy Pup" on "another board".
Properly Winterizing a structure:
"While one might think that draining the water distribution system is easy, in actuality it really requires a thorough understanding of plumbing layout to insure that no water will be inadvertantly trapped in a line somewhere. While there are some fundamental basics, in reality every structure will ultimately present different problems.
As you go through the house make a list of all lines or valves that you open. If you are not going to be the one to later restore the service, leave the list posted in a conspicuous place so whoever does the startup will have a heads up on what is disconnected.
First begin by having the water turned off at the street main by the local water utility company.
Begin at the uppermost floor and open all faucetts to allow all standing water to drain, then leave the faucetts open to vent air in as you continue down floor by floor opening faucetts. Do not forget to open the hose bibbs.
Disconnect the water heater electrical service or turn the gas valve off. Attach a tag to the breaker panel or gas valve indicating the water heater vessel has been drained, then open the water heater drain and disconnect the union on the hot water line to allow air to vent into the tank to aid in draining.
If the house has a basement where the lines are accesssible, physically walk the lines and look for stop and waste zone valves, and open the waste ports.
Pay particular attention to areas where a pipe may drop down then rise up again forming a low area in the pipe that could trap water. In the case of copper or CPVC lines sometimes it is necessary to cut the line, then install a coupling to repair the cut. Pay particular attention to pipes in a crawl space because often they are in an out of sight out of mind position and may lack the proper pipe hangers.
Disconnect all faucett supply lines and make sure the faucett is open to insure all residual water drains.
Turn the water main off (valve on the street side of the water meter) and disconnect the water meter at the mount unions. If there is a shutoff valve on the house side of the water meter leave that valve open.
If the house has a well and home water pump make sure the electrical power is turned off and tagged out,then check the pressure tank and any expansion tanks to insure they are drained.
Mix some "food grade anti-freeze" 50/50 with water. (Food grade antifreeze can be purchased at camper supply stores for use in campers and motor homes.)
For the kitchen, bath and laundry sinks you can disconnect the P-trap and leave the disconnected trap in the sink as a visual indicator, otherwise pour about a pint of the anti-freeze solution in the drain to protect the traps.
Pour about a pint of antifreeze in the tub or shower drains as well as any floor drains.
flush the toilet tank and use a closet type plunger to force as much water out of the trap as possible, then pour antifreeze in the bowl.
Thoroughly dry out the inside of the toilet tank with a sponge and a rag.
If the house has steam or hydronic heat first turn off the gas and tag it to show the boiler is drained.
Disconnect the electrical service and attach a tag to that as well indicating the system is drained.
Tagging out heating systems or water heaters is vitally important because if the heat source would happen to be turned on for even moments without water in the vessels it can do permanent irreparable damage to the unit.
I took a preformed 3/8" pex faucett supply line and cut the faucett end off, then i spliced the line onto a short air hose that will attach to a small air compressor. I can then quickly attach the line to an angle stop and use air pressure to insure all water has been pushed out of the line.
Drain the boiler and associated hydronic pipeing.
When you are done, take a few minutes to retrace your steps to make sure you have not overlooked any point of water demand in the structure.
Keep in mind that when winterizing a water system "Murphy's Law prevails, what can go wrong, will go wrong. In all probability no matter how much attention you give the system subzero temps will point out a place you overlooked.
,the steps I outlined are how to do it correctly..I could offer you a dozen methods to get in and out fast, and probably be 90% ok...but from experience, when i have to go in an do a startup if it was not done in the manner i described I will normally have a days work repairing water lines.
I just did a fourplex apartment structure in Masury, Ohio that was signed off as winterized...when we got to water service turned on we found 112 leaks, all resulting from fittings pushed out or pipe walls ruptured from freezing, not to mention we found 4 electric water heaters burned out because they drained the vessels and never turned the breakers off, so when the power was turned on the heating elements immediately burned out."
Hope this information proves helpful to you next season.