a person employed to pump out and clean septic tanks or portable toilets

The act of giving someone fellatio, while submerged in a bath tub. Stipulations include, the giver wearing a snorkel, and the receiver defecating a floater so it bumps into the givers head, effectively acting as the shark.

What Olivia and claire are (you know who you are)

The act of having anal sex and during the removal of said cock pulls out a shit shark on the end

A Shark Shit is the disgusting act of someone swimming at the beach that is too lazy to get out of the water and use the public restroom like a normal person, instead they take a shit right there and then in the ocean.

how low can you go?
you cannot get any lower than shark-shit, because it's below sea level.

metaphor: To defecate any of numerous elongate mostly marine carnivorous fishes with heterocercal caudal fins and tough skin covered with small toothlike scales.