maribating

The act of masturbating in the bath tub then proceeding to soak (or "marinate") in your own juices

After a long day of work, Ben spent a solid 3 hours maribating, and never felt better.

Brendan: "hey, is Ben coming out tonight?"
Amanda: "nah, he's got a full night of maribatin' ahead of him"

Kirstyn: "ben, your skin is so soft! Do you moisturize?"
Brendan: "nah, he's a chronic maribator"