Installing bathroom sink - drains off slightly less than pipe diameter
The Fernco Flexible trap seems to be working. It does say on the package it is safe to use with typical bathroom chemicals. I don't use chemicals, however (package also says most stoppages within the trap can be solved simply by squeezing the trap, although I'd remove trap & clean out rather than risk simply pushing the problem further downstream). At $4/trap (plus $4.50 shipping), you could easily replace this thing every 10 years if you were nervous about any potential for leaks. The biggest danger, I think, is pushing things in the vanity underneath up against the trap & causing some kind of problem.