Tubthumping

"When you take a dump in the shower and it lands with such impact that it creates a thumping sound." Tubthumping.

"Did you see the state of Gary at the weekend? He's such a tubthumper."

Past tense: Tubthumped.
Future tense: Will tubthump.

I accidentally mixed up my medication and laxatives, found myself tubthumping for a good few minutes.