Where are they?
There's not a single object that looks like a Shitter on any of the ships.
Granted, they could just drop their pants, sit on a railing, and empty their mortar's clip into the ground, but with all the different hazards of just being in the air, there's no way they rely on relieving themselves like that. Plus I'd think you'd fall off the ship.
And there's no way the absolutely insane people of GoIO don't find a way to harvest the power of human waste.