I bought a house new in 2004. The basement was plummed for a future bathroom. There is a 2" bath drain pipe coming out of the slab in a square tub box, a larger drain out of the slab for the toilet, and there is a drain coming down the wall from the upstairs plumming for the sink. It has a capped off "T" split to tie into. My question is, how can i tell if the tub and toilet are tied into a vent? If I tie the sink into the T split from the upstairs plumming, can i assume the sink will have proper ventilation? Am I going to have to tear up the concrete to vent the toilet and bath? It seems like the builder would have done this before pouring the concrete however I cant ask them because they went out of business of course!