This is for two gay men. The giver gets a boner and swipes it across the asshole of the taker getting some poo on the end of his penis (this is the rust). He then lays his boner between the ass cheeks of the taker like a hotdog in a bun. After he's aquired this task he pees on himself finishing the bubbler part of the name. Hence, the rusty bubbler.
I'm so gay let's do the rusty bubbler.