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.
Tank is being drained as we speak.
My taters luv me!!
Heck, might as well put it to good use.