Litter box is fine, he was just going to hang upside down from the ceiling and shit on her floor anyway.
Needs the shower though, have you tried to shit while hanging upside down and not covering yourself in it?? No chance.
Seems like an oddly detailed thing to say, perhaps drawing from life experience? (If so, ngl, kinda impressed)
Also
Still more civilized than how he usually does it from the rooftops intentionally missing the drain aiming at filthy poor pedestrians Gotham scum.
Imagine a crime free Gotham. Living in fear not of a Batman that caused physical harm when he catches you breaking the law, but he does follow you around peeing on you until he finds another crook.
Iirc the manga did have a VERY similar moment I wouldn't be surprised the Doujin is inspired by.