Back in the mid 70's I played in a casino band with a very talented trombone player. The guy practiced all the time. And through years of diligent work he became able to contort his embouchure in such a way that he could make a variety of incredibly authentic fart noises with his trombone.
Everything from a soft little squeaker to a big raspy boomer like you'd hear in a Denny's restroom when they were running the baked bean and cornbread lunch special. He would occasionally let out a little fart noise during the comedy routines whenever a joke bombed. Then he started making the noises during the musical numbers whever there was a break in the horn parts. Everybody in the band had to fight to keep from cracking up. But after the second night of this he was let go. Whenever I hear slap bass it reminds me of those fart noises coming out of his trombone. Slapping and popping adds as much to the music as a trombone fart. But of course that's just my personal opinion. Apparently most people love hearing those sort of noises coming out of a bass. But to me it's like fingernails being scraped down a blackboard.........and about as useful as a trombone fart.