Water heater flush yielded almost no sediment
In addition to the answers above, I have backflushed mine by hooking up a washing machine hose (double female) and turning the water on and off.  I am on a well and I have a good filter system, so I rarely have much-unsuspended junk in my water.  Home Depot has a scope (Ryobi?) that allows you to look into the water tank through the lower element hole.  It has many uses, like you can do your own colonoscopy!  Lol!