If you’re at a house, the sink is always behind the door which is the context this rings true to me. Or if you are waiting outside a commercial single occupancy bathroom. Those used to have men and women signs but today often times they’re not gendered.

I went to one bar once that had private cubicles with no sink inside, and a shared sink for everybody.

I guess I’ve never seen a “cubicle” with a sink inside but I have seen single occupancy bathrooms.