Sidi shoes

"Toilet" is the act of washing oneself- one attends to ones toilet in the bathroom.
You have a crap in the lavatory.
Although, thinking about it, lavatory originally meant to wash also.
SO- Thunderbox it is. That has no other meaning to confuse the issue.

One can do whatever one wants wherever one wants but one can expect to be called a posh knobber whilst one is doing it, innit.