Top Definition
The act of two people making out with such fervor that it is audible to others around.
Example 1:
(Josh and Lana are making out)
Marlee: Can you hear that?
Amanda: Is that the fish tank?

Example 2:
(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)
by curlyfries102 January 30, 2011
Term used for those who cruise in a convertible with the top down and the windows rolled up. A car in this configuration appears like an aquarium or fish tank, especially after a good rain storm.
Check that geek in the Miata, he must be fishtankin it to keep his wig on.
by Skizix June 21, 2004
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