The act of utilizing chewable breath mints and diet soft drink to produce a violent eruption of carbonated water from a vagina. Useful in retrieving items jammed up against cervix during the practice of cannon fodder.
I jammed Mentos and Diet Sprite up her cunt to get her to do an Old Faithful.
by Profane Urbane November 06, 2010
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Top Definition
An old faithful is upper-decking taken to the next level. Here are the steps:

1) Remove lid from toilet
2) Flush toilet, then grab black floating ball in the tank before the bowl refills. Hold the ball there for now. The bowl of the toilet should be empty.
3) Fill the bowl up with vinegar
4) Pour about 5 boxes or baking soda into the tank
5) Release black ball, so the baking soda mixes with fresh water, and replace the lid. - leave, watch, and wait.

When the next user of the toilet takes a shit, the vinegar and baking soda mix to make what can only be described as a shit volcano.
I took a shit in my friend's toilet. When I flushed, it overflowed into a foamy brown mess all over the bathroom floor. It was then that I knew my friend was a victim of Old Faithful.
by moustacherocker July 25, 2006
Double Chin
Kelly, your old faithful is showing.
by yo mamma>dayum straight February 02, 2009
While a girl is fingering herself, she lifts her lower body in the air. Then, as she squirts, it looks like a geyser spraying up into the air. As the squirt juice falls back down, the girl then flails around with great passion as she is covered with her own squirt juice.
Guy: Why are you so sticky?
Girl: I just got done doing an Old Faithful.
Guy: What the fuck?
Girl: Yeah, I do it EVERY time I masturbate.
by Haywood Jablowmii September 06, 2012
this is when the male ejaculates in or onto the anus of a female, she then farts and the jizz shoots up into the air, resembling the geyser, old faithful.
Jose: I got bored last night so i gave Jen the Old Faithful

Mike: Nice, ill test it out on Brittany
by Jack10392 May 06, 2010
The act off nutting (ejaculating) inside someone's mouth while they are on their back then stomping on their stomach. Those wearing a Used Poncho can avoid the geyser's angry eruption.
My girlfriend took one in the mouth from me last night so I stomped on her stomach, thus completing the Old Faithful. Wish I would've had a used poncho on...
by Brettford January 07, 2013
A sexual act. It is when you pour an entire bottle of lube into a girls ass. Then, upon the first thrust, the lube sprays out like a geyser.
"Whats all that lube for"

"Yellowstone, here we come, Old faithful, baby."
by AsevenX88 August 13, 2011

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