To urinate in a persons rectal cavity. Can be followed by "siphoning" in which a hoselike object is used to siphon out the urine.
After John gastanked Jill, he proceded to siphon out the urine with a straw.
The act of farting inside of a car and locking all the windows, making the people inside suffer.
Fred: Why are you looking at me like that? What's that smell? Holy mother of god, not a gas tank
You are stuck in a gastank when someone cuts a fart in an enclosed area, like a car or an elevator.
The drive to the beach sucked because Hugh had some serious beer farts and it was raining. I couldn't open my window and my eyes were watering in that gastank.
The act of a women giving oral sex, but instead of spitting or swallowing she just lets her moth fill up with the mans cum.
Dude, your girl just gave me a gas tank.