Yumm, sewer gas. What, no P-Trap. Somebody’s tub drain isn’t working.
Getting the feeling that if someone ever did this they have much bigger problems than not having a bong handy.
This reply serves as a +1 upvote to your comment. I’m no pro plumber, but something is wrong with this diagram – not the least of which is that someone is so addled in the head as to think that this is possible, much less desirable.