Quite correct about it being a slow leak... started out slow, 2 days ago.
It was slow enough I could still pressurize the tank (years ago I learned from experience to have a cold-water shutoff before the tank!) and turn on the breaker, could still take a shower.
Last day it has sped up quite a bit, so now the water is off and the 240 is disconnected.
With any luck by noon or so the new one should be in. As long as I can get a good drain on the current one...
Draining can be a messy project and the pan canhelp you here.
If it goes slow or not at all you need to shove a coat hanger in the drain bib to loosen things up..The new pan under the bib will catch any thing that comes out when the hose is disconnected and reconnected.Have lots of towels and mops ready
Also if its slow and/or once it starts to run turn the inlet on and off full blast to help loosen the crap up.Some times this helps,sometimes.
Also you can shoot water into the drain (reverse connector and use adapters) As another poster mentions Its heavy but if need be get a hand truck and roll it out.Not sure of your living arange ments.
If its in the basement and you have a floor drain and the drain on the heater is plugged turn the old one upside down next to the drain and enpty it.At least it wont weigh 300 pounds.