Stuck live well cover

[onthefly]

My 1999 SeaCraft 20' has an external screw-off disc plate to let the livewell water flush and to keep things like shrimp kickin' without the noise of the pump running. (They all turn pink at the dock over night, so obviously it doesn't refresh when just sittin'.)

My question is, how do I keep it from sticking shut when the boat sits for a week or more? The "handle" (more of a finger wide/tall bump) on the doesn't have enough leverage, especially hanging over the transom, upside down, swearin' a blue streak...Grease didn't seem to help. Silicon seems to wash away.
Thanks.