He also owns all of the grocery stores, food distributors, trucking companies, farms, laborers, and politicians to remove safety laws and taxes concerning all of those, for a better analogy.
The vent is to stop vacuum from forming behind your water traps when someone else flushes on the same drain line. There shouldn’t be any real amount of decomposing waste in that pipe permanently, it should wash along to sewer or septic tank. The vent pipe definitely has enough to breath but one can only imagine the smell or taste.
Skilled paid stonemasons were required to build the tight fitting surface stones of this one, so some of the laborers were definitely not slaves, howeveri believe you’re correct I doubt the sled drag team was salary.