bathroom

A flush toilet would use a heck of a lot of water and would suck your drinking water tank dry quickly. And fill up your black tank. So you would be stuck camping only with FHU like those with residential refrigerators.

Further thought: the tank of a flush toilet is not very firmly attached to the bottom of the unit and I'm not sure how well it would hold up to cross-country travel, driving down I-10 in Louisiana for example. And the whole thing is made of very breakable porcelain.