slap the basin

To hit the toilet bowl with an enormous log of poo effectively slapping the basin of the toilet bowl.

Hey! did you slap the basin? It smells like shit in here and the toilet is brown.

Slapped the basin

To take an enormous shit and have it hit the toilet bowl aggressively.

I had a bowl of chili last night, and this morning I slapped the basin. Now somebody needs to fix the toilet.