Deep sea snorkelling is similar to the original snorkel. However, when the giver of the snorkel licks the guys balls and wanks his cock, s/he takes a deep breath and goes down further. Often including rimming of the receiver's anus. Thus looking like a deep sea snorkeller.
Suzy's boyfriend had an especially fantastic orgasm when she began to snorkel him and then surprised him by taking it further and indulging him in a session of deep sea snorkelling.
A turd that 'scribbles' on the bowl as it goes down... leaving indecipherable markings that clearly convey a message to those who follow along, even if a literal interpretation escapes them.
An underlying implication is that it's a massively smelly example that will surely 'kill' the sea to which it is no-doubt heading.
"Dude, someone just left a dead sea scroll in the can on our floor... I'd suggest using the one on the 5th floor unless you're ready to tackle the next chapter in sanskrit..."
A beautiful novella by Ernest Hemmingway that describes the trials of an old fisherman who goes out too far and catches the biggest fish he's ever seen. They say there are refernces to Christ in it.