Tiana Abney tells TMZ about how she and her partner Logen went from joking about it to actually saying "I do" in the famous "disco bathrooms" of the HOP Shops convenience store in Verona, KY ... pulling the whole thing off in a matter of 3 weeks.

They tell us the gas station didn't just provide the venue -- on Valentine's Day, no less -- they covered the whole shebang, with expenses totaling between $700 to $800!

And, if that wasn't sweet enough, they threw in a wedding cake!

As you can see by the pics, there was quite the turnout to Tiana and Logen's bathroom ceremony -- from parents and siblings to friends, cousins and coworkers, everyone they knew seemed to be there.

The gas station even closed the restrooms for a whole 2 hours to accommodate the ceremony ... offering free fountain drinks to other customers as a token of appreciation for the inconvenience -- which seems counterintuitive when ya can't go pee, but a nice gesture, nonetheless.

There is a limit to the HOP Shops hospitality, though ... no lifetime discounts for the newlyweds. With the price of gas, that would've been the ultimate wedding gift!

On its website, HOP Shops bragged the wedding is a reminder "love knows no bounds and that true romance can be found in the most unexpected of places."