When you nut inside your partner without a dome.
Alex B: Yo, do you have any domers?
Mike P: Nah, just fill tank man.
by Union St November 8, 2017
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To shit in the back tank of a toilet, after removing the cover. This is best done in a public bathroom, as the turd(s) will not likely be found for several weeks, despite the pure, rancid stank it will emit. Due to the general orientation of the toilet tank and the wall, this can be a difficult task, and any successful attempt should be properly commended.
Stephon: Any needledick can shit on the floor at Wendy's; it takes skill and grace to fill the tank.

Crew: roflberry pwncakes
by J Hate May 27, 2006
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The act of expelling urine into a woman's asshole. Often brought about when asking "May I pee in your butt?".
Did you hear about last night? Tyrone ended up filling the tank with Shelly to the point where she was dripping oil for 3 hours
by Keith ac May 20, 2008
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when you blow a load in a girls mouth, much like filling the gas tank on your car.
by Kyle December 25, 2003
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To shit in the back tank of the toilet after removing the cover. This is best done in a public bathroom as it may not be discovered for weeks, despite the pure, rancid stank it will emit. Due to the orientation of the toilet to the wall, this task is often difficult, and any successful attempt should be properly commended.
Stephon: Any needledick can shit on the floor; it takes skill and grace to fill the tank.
Crew: roflberry pwncakes
by J Hate May 27, 2006
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Filling the gas tank is when you stick your dick into someone's ass (male or female) and proceed to piss.
Cade: I got laid last night.
Owen: Yeah right, by who?
Cade: Bronwynn let me try Filling the gas tank
Owen: 🅱oi
by Loaf of Beans June 12, 2018
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Person A: I went home with that girl last night.

Person B: Did you "fill the gas tank"?
by tabittle August 6, 2009
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