Our water heater is at least 17 years old, and it’s never been drained. I replaced both elements and thermostats and was not able to drain it, which lead to a draining via the element holes, not fun. I tried to suck out some of the sediment, but that was a bitch itself. I bet there’s about 4-5inches of sediment still in my water heater tank. I have so much sediment, you can open the drain valve and nothing comes out! Empty out your water heater tank at least once a year, it’s preventative maintenance!!
Update: Also, don’t turn on your water heater if it’s empty it’ll ruin the element and you’ll have to replace it again…I learned that the hard way!