My bus was owned by a blues singer before I got it, he had it converted by the Caldwells, they are a very respected professional conversion company, the black water tank had a straight drop out the bottom thru the bottom of the bay floor, controled by an air switch on the dash lol, the vent also went straight down thru the floor, I've been piling sawdust in buses, motorhomes, travel trailers and all sorts of rvs in between for years, I've seen probably every concievable combination of factory venting including a system years ago that fed the contents of the black and grey tank into the exhaust system that supposedly burned them creating a no dump tank lol. I realize the codes are there, I also realize that they tend to have a way of getting around them as the engineering needs dictate at times.
Builders of entertainer coaches have their own code book, which they keep a top secret.
I have torn into a few of them myself, their theory seems to be that rules only exist to be broken.
I mentioned here a couple of years ago about the tank drains straight out the bottom with no hose connection, and the response was that it was ridiculous, nobody would do that. The driver typically dumped the tanks going down the Interstate at 2:00 A.M.
Generally, the rules are no poo on an entertainer bus, but stuff happens.