Similar to the rusty trombone and rusty trumpet, this sexual maneuver is a collaborative effort. It requires four people: one man, two skinny women, and one fat one. The fat woman gives the man a rim job while giving him a handjob (the rusty trombone). The man gives one skinny woman a rim job while fingering her clitoris (the rusty trumpet). This woman does the same for the last woman (the second rusty trumpet). This last woman also gives a good rim job and fingering to the fat woman (the rusty tuba).
Man, the rusty brass quartet just seems like it would be awkward to perform. I'm not even sure that's a real thing.