My longest running thread is over at the Livclean Department. It's been going on forever! One thing I did learn is that you should flush a new hotwater tank regularly, perhaps Spring and Fall, or more often if you are neurotic. You'll see a nice brown sludge coming out.
Now, if your tank is over 10 years old and never been flushed, I'm not saying to touch it! It is a ticking time bomb ready to explode, and if you flush it -- KABOOM! (maybe). I just don't want all the whiners coming back and saying: "Mr. Fish, you blew up my tank!".
I'm surprised how many people do not make provision for the tank cracking. I've had two crack on me, and luckily I have a direct drain. Somebody I know had all the finished basement ruined. And the same goes for washing machine hoses! Never--ever use the black rubber crap that may come with a new machine. Go high-end on this, trust me!