The act of two people making out with such fervor that it is audible to others around.
(Josh and Lana are making out)
Marlee: Can you hear that?
Amanda: Is that the fish tank?
(Alexander and Kayla were making out the previous night)
Alexander: (sly look) So, I kept hearing a belt buckle last night...
Nathan: Yeah well, I heard you fishtankin' it up! How about that?
Alexander: (holds head down in shame)
Nathan: (ultimate glory)