Can drain out bathroom be used in a toilet? Open the drain valve and empty the water heater into buckets or down a drain sometimes opening a hot water faucet on a sink helps the water heater tank to empty faster. Thank you so much for assigning a positive, knowledgeable, and efficient technician for our furnace time-up! he represents everything we love and have grown to expect from holt! If you are considering replacing an old boiler. Clean blockages.