You are standing beside the water heater with a bucket and a garden hose, and the tank has not been drained since it was set. This walk-through is for that moment. It sorts the flush into the parts you can do, the parts that belong to a licensed trade, and the points where you stop and call.
What a flush is for
Hard water leaves mineral solids on the floor of the tank. Over time that layer settles under the burner or the lower element, where it holds heat in the wrong place and can make a normal tank run noisy. A flush clears the loose part of that layer. It does not replace a worn tank, and it does not repair a tank that has already started to leak. Most manuals give a drain interval. Use the figure in your own manual, not a number from a website.
Owner work
You can usually handle the drain itself without a license, as long as the unit is in good order and you follow the manual. Start by shutting off the power at the breaker for an electric unit, or setting the gas control to pilot or off as the manual directs. Let the water cool first. Hot water scalds, and a full tank holds real pressure.
Close the cold supply valve at the top of the tank. Attach a hose to the drain valve at the bottom and run the other end to a floor drain or outside. Open a hot tap somewhere in the house so air can enter the tank. Then open the drain valve slowly and watch the first pull. The sediment you see in that first flow tells you how much is in there.
When the flow slows and the water runs clear, close the drain valve. Open the cold supply briefly to stir loose sediment, then drain again. Repeat until the water runs clear. Close the drain, remove the hose, and open the cold supply fully. Let the tank fill, then open the hot tap until the air sputters out and the flow runs steady. Only after that should you restore power or gas.
Where the job stops
Stop if the cold supply valve will not close. Do not force a drain valve that is crusted, leaking, or stuck open. If the flow stays weak or sputters after a full flush, the problem may be past what a drain can fix, so call a plumber.
Leave the gas line, the flue and venting, and any relief valve replacement to a licensed plumber or installer. Electrical connections and thermostat work belong to a licensed electrician. Element replacement may fall to an owner in some places and not in others, so check your local rules and the manual before you decide. Keep the work general to the tank, and treat anything that touches the connections as a hired job.
The question to ask before anyone opens the tank
If a service plan covers the tank, read its visit terms before you assume a flush is included. Ask whether routine flushing counts as covered maintenance, who is allowed to perform it, and whether the provider requires its own technicians. Some plans also ask you to keep records of past service, so keep the manual and any receipts together. Nothing in a plan is a promise about how a future claim will be handled, so read the written terms rather than relying on a verbal answer.
How to decide
Compare four things. Does your manual give a drain interval, and is the unit due? Is the drain valve free and able to close fully? Does the job stay within the tank, or does it reach the gas line, the venting, or the wiring? Does any service plan require a visit by its own network? If you can answer all four plainly and the answers point toward the tank alone, the drain is yours to do. If any answer is unclear, hire the job out, or ask a plumber to check the drain valve on a visit they are already making.