Removing Atwood water heater plug photo added

Older model Atwood drain plugs needed a 7/8" socket/wrench
Then in 2004? the drain plug size changed to 15/16"

6 point socket works best

I use our 4 way tire iron. One of the sockets fits perfect no muss no fuss.

15/16 socket and extension
Do not use anything other then the nylon hollowed out plug from Atwood.

I have the same experience as you, I have used a box end wrench, forget the size but still only 1/8 of a turn.
I plan to get a set of ratchet wrenches, maybe then I can do it easier.
I did replace the plastic plug with a brass one from camping world that has a drain cock similar to a car radiator drain, at least now I do not need a wrench to drain.

Socket with an extension