[RandomBacon]

They should install a gravity switch. A simply contact that uses gravity to either remain normally-open or normally-closed, and then when the opposite is true, automatically flush.

[InitialLastName]

Open question: to what extent does the flush mechanism in airplane toilets rely on the presence of gravity?

[account42]

It quire clearly uses a pressure differential to quickly suck your shit out of the bowl. I doubt gravity makes much of a difference.