suck the septic tank

Two meanings:

1:A person 'drug addict' that would do anything for a hit/high.

Desperate times call for desperate measures.

Meaning everyone goes to the toilet, so perhaps someone had drugs In there system.

2:a person who uses sexual acts as a way to get through life.

1:
"He'd suck the septic tank if he could"

"Have you seen that guys mum, so feral she'd suck the septic tank if she could!"

2:
"How did she get that promotion? Don't worry she'd suck the septic tank if it meant getting ahead"