My showers have not been lasting very long lately, and I love my hot showers.
So I got to looking into water heater maintenance. Today I finally took the plunge and flushed the water heater. It turned out not to be too hard. The only mistake I made was at the end while refilling the tank. I left the pressure release valve open, and subsequently flooded the basement. (Note to self: next time just leave the hot water faucet open and closed the valve before refilling the tank.)
I don’t know if this is going to fix the problem. I might try a shower tonight and see. But I suspect the real problem is that the dip tube inside has broken or come undone. But disconnecting the cold water inlet to look for the tube seems (right now) beyond my ability.
Update: So I have actually created a new problem: the pressure relief valve is leaking. From what I’ve read online, it seems that when you open an old one, frequently is doesn’t shut back down the way it’s supposed to. Hooray. Looks like I’ll have to replace it.