If your house is to be vacated during cold weather and the heating system turned off, follow this procedure:
Shut off the water supply at the main shut-off valve at the street. Then beginning with those on the top floor, open all faucets and leave them open. If available, open the cap on the main shut off valve drain the remaining water. Remember to reinstall this cap when complete. Shut off and drain all hot water tanks. Make sure all horizontal pipes drain properly. Air pressure will get rid of trapped water in these pipes, but occasionally the piping may have to be disconnected and drained. To be safe have your plumber check your entire plumbing system.
Remove all water in the p-traps under sinks, toilets, bathtubs, and laundry, use a wet vacuum or other method to siphon the water out. Sponge all the water out of the toilet tank and bowl.
Fill all traps with a DEQ approved non-freezing solution such as mineral oil, windshield washing fluid or RV type anti-freeze.
If your house is heated by hot water or steam, drain the heating pipes and boiler before leaving, following the equipment manufacturers recommendations.
Note: When you return home, refill all the systems BEFORE lighting the hot water heater or boilers.