How to Flush a Water Heater Tank

For a gas water heater, turn the gas control valve (the box on the front of the tank with a temperature dial) to the "pilot" position — this keeps the pilot light lit but prevents the main burner from firing while the tank is empty. For an electric water heater, flip the dedicated breaker in your electrical panel to "off" and verify it's dead with a non-contact voltage tester. Never drain an electric water heater with the power on — an exposed heating element will burn out within minutes.

Locate the cold water shut-off valve on the pipe entering the top of the water heater — it's usually a ball valve with a lever handle or a gate valve with a round knob. Turn the lever perpendicular to the pipe (ball valve) or turn the knob clockwise until tight (gate valve). This stops new water from entering the tank while you drain it. Confirm it's off by opening a hot water faucet upstairs — the flow should slow to a trickle within a few seconds.

Open the hot water faucet at the nearest sink or bathtub and let it run for 10 minutes. This accomplishes two things: it reduces the water temperature inside the tank from scalding (120-140°F) down to a safer range, and it begins to relieve pressure so the tank drains faster once you open the drain valve. Leave this faucet open throughout the entire flush — it acts as a vacuum break that lets air into the system so water can flow out the bottom.

Locate the drain valve near the bottom of the tank — it looks like an outdoor hose bib with a 3/4-inch male hose thread. Screw a garden hose onto the valve hand-tight, then snug it a quarter turn with an adjustable wrench to prevent drips. Route the other end of the hose to a floor drain, utility sink, driveway, or any area where hot, sediment-filled water can discharge safely. If draining uphill or a long distance, gravity alone may not work — in that case, drain into a 5-gallon bucket and empty it repeatedly.

Turn the drain valve counterclockwise to open it — plastic valves have a handle you turn by hand, while brass valves may need a flathead screwdriver in the slot. Water will begin flowing through the hose. The initial flow will likely be cloudy or rust-colored with visible sediment particles — this is normal and exactly what you're flushing out. A full 40-50 gallon tank takes 20-45 minutes to drain depending on hose length and gravity. Let it run until the flow slows to a trickle.

With the drain valve still open and the hose still attached, briefly turn the cold water supply back on for 15-20 seconds, then turn it off again. This burst of incoming cold water stirs up sediment that settled on the bottom and pushes it out through the drain. Watch the hose outlet — the water will turn cloudy again as sediment flushes out. Repeat this on-off cycle three or four times until the water running from the hose is consistently clear with no grit or discoloration.

Turn the drain valve clockwise until fully closed — firm but not overtightened, as plastic valves crack under excessive force. Open the cold water supply valve fully and let the tank refill. You'll hear water rushing into the tank. Keep the hot water faucet upstairs open — air trapped in the tank and pipes will sputter out through this faucet. Once the faucet runs a steady stream of water with no air bursts, the tank is full. Close the faucet. Unscrew the garden hose from the drain valve and check the valve for drips — if it weeps, wrap the threads with Teflon tape or replace the valve.