Hi ---I am converting an upstairs bathroom into a laundry room. So far I have gutted the bathroom and made some holes in the floorboard to check the layout of the drain and supply lines. There is a 1 1/2 inch vent pipe connected to the main drain line( 3" pvc pipe) that seems to be there for no purpose. It may have been there to somehow service the shower that is no longer there.
** My question is this....I purchased 3" couplings along with some 3" pvc pipe so that I can remove the section with the vent lines attached but I not sure how to make this patch since the lines are inplace. Is there a trick that the pro use to make this type of tight connection? If there is I would greatly appreciate some insight.

**Secondly, this bathroom shares a common wall with a second bathroom and non of the fixtures seem to have a separate vent...there is a 3" main vent stack within 4 feet of all fixture....is that the reason that there aren't any vent stacks? If I add the washing machine to this setup, will it still be ok...there will be a 2 sinks with 1 1/2 drains, a bathtub and a washing machine with 2" drains, and a toilet that will all be connected to this one main vent.