tricky? From what I know, the procedures should be:
1. turn off the house water.
2. open up one of the hot water faucet.
3. drain the water heater (with a garden hose hooked on).
4. cut off the old valve and solder on a new one.
Is there anything that I need to be really careful
One of my concern was that: since I never drained the water heater,
it might not be able to drain. Also, if it drains, it might not be closed
again due to old seal. Is such thing common for a 9-year old water heater?