Flexible Boot for Air Vent

I have someone who is installing a medicine cabinet. When he cut a hole in the wall, there was a cast iron air vent pipe blocking the site for the cbinet. His solution was to cut the pipe to remove the section that is in the way and then rejoin the pipe using a (rubber) flexible boot. My question is whether this will become a problem later. In fact, I have read that it is against code to install a boot behind a walll. Is that only in the case of water pipes? Does it also apply here for a vent? Is trouble on the horizon? Thanks.

Vent/drain pipes above ground can be joined with no-hub connectors. THese are neoprene rubber sleeves with metal reinforcement bands and all secured with hose clamps. If the fitting was just a thick rubber sleeve with clamps at the end, it is not to code.

Air doesn't really care about the corners, but jogging it over will make it impossible to run a snake down if it ever got clogged by say a dead bird, mouse, squirrel, leaves, etc. Any horizontal sections need some slope so any condensation, melted snow, rain, etc., can drain without blocking the pipe.

What you saw is one reason why many medicine cabinets are surface-mounted, or the wall is bumped out.

Thanks. Actually the cast iron pipe is horizontal in this section too! I am mostly worried about the lifetime of the boot.

If the proper one was used, it should outlast the pipe.

Is this pipe truly a vent (air only) or, is it a drain line that has waste water run through it?