I don't have a greyhawk but I can drain my water heater thru one of the low point drains (cold water system drain).
My WH doesn't have any check valves so it will flow back thru cold inlet line and out low point drain .....just have to open kitchen faucet hotside (closest faucet) to allow air back into system.
But removing drain plug is just as easy
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31