poorly plumbed drain belching hot smelly air

[garbanzo]

i recently bought an apartment in Budapest. it's an old Soviet pre-fab made of cement panels, so changing plumbing is very problematic. it's therefore common for people to retrofit a washing machine into the bathroom. water supply lines are easy to tap into, and usually, people just drop the drain hose into the bathtub when doing laundry.

i checked the plumbing when i bought the place and was satisfied, but after a few days of working on it, i realized i overlooked something. the previous owner recently tiled the bathroom, and it seems that when he did, he put a pipe under the bathtub that sticks out next to the washer - i didn't notice this at first. because the washing machine hid it. i assume it is meant to be a drain for the washing machine, but the washing machine drain hose wasn't in it.

there is a very small access to the space beneath the tub, but it's under the sink, and i can't even look in there, let alone work in there. i got my wife to peek in with a flashlight and tell me what she saw. apparently the drain pipe the previous owner put in is patched straight into a main drain, and there is no P trap in it, so the drain is venting straight into our bathroom. it's not very nice at all! and i can't fix it without tearing out a lot of tile, which i'd rather not do.

so here's my question - can i just cap this pipe where it comes out of the wall? will that pose any problems? i don't know how much pressure there is in the drain system, but this is definitely where the smell is coming from, because all the other drains in the apartment don't smell. sometimes i can actually feel warm air coming out the pipe.

thanks to anyone who reads this and can give some advice!

[PLUMBILL]

Yes, just cap the pipe however; if all the pipe joints and connection at the main are not water/air tight this problem you are having can occur again.

[garbanzo]

ok thanks for the feedback. i flushed the drain line with bleach and hot water the other day and there was no sign of leakage so i think all is well.