Did Diane mean the "convenience store" aka The Dutchman, where teapot jeffries simmers in an old motel room guarded by bathrobed wearing, bosomy entities?
Or did she mean Big Ed's gas farm? Where weird, burning rituals occur and glitched out reflections exist?
I assumed she was talking about the convenience store (which indeed has a couple of gas pumps). To say the truth, when it was shown in S03 for the first time, I thought it was a gas station until I saw the sign reading "CONVENIENCE STORE".
In some places gas stations function as convenience stores...
Gotta be the Convenience Store. Leading to the obvious question of where's the original Diane.