Ok so I hired my friend who is a plumber to run my lines and setup the drain for my sink. Its a 10 year old house so everything was in place, for the drain I guess he just removed the cap and added the elbow to attach the P trap to. So I installed the sink and it wouldn't drain! My 'friend' (basterd!) won't call me back so I'm left to hire a plumber or troubleshoot myself. After sticking a snake down there I could feel that there is a cap or something blocking. I tore a bit of sheetrock out so I can get a better visual of the setup. It appears he got rid of the cap where my sink is which was just to the right of the vent, but apparently he didn't check further down the line to see if there was another cap. I reached in the wall with my hand the same distance as the snake went and noticed a coupler.....so I guess the original builder capped it then installed the coupler and the drain line and vent...is this common? To a layman such as myself I'm guessing this was done so if there was a back up it wouldn't back up all the way there and up into the vent...I dunno.
Anyways it seems I am left with 2 solutions I was able to come up with....I can tear more drywall and cut the pipe between the main and where I'm installing the sink and install a new pipe that isn't capped.....this would include tearing up drywall in the bathroom and an adjacent closet and shelving I just installed...adding more time and money of course. Or the other is I can get to the cap through the pipe (as it is just 16" away) with a spade bit and extension and drill through this cap, I would also be able to run water through after and reach my hand to ensure I didn't create any leaks.....I am hoping for a professional opinion before continuing.