Good question @OrvilleBrandenburg
The answer could possibly be yes, BFDI characters can canonically use the bathroom but since they're inanimate objects their systems could be different from ours. (Idk if it was shown in BFDIA 14 PointPointyPointy but someone correct me) Pin was shown getting outside a restroom while looking around, I don't know in what episode it was shown nor it it's a clip. So the answer is technically yes.