There is an easier solution. they make a one way vent which you can connect to the waste line in the wall. Not sure whether you are taking out the wall to move your sink or not. I just got done completely redoing a basement bathroom and I had the same problem, I couldn't tie my relocated sink into the existing vent. So the plumber installed a tee in the line after the trap and then put approximatly 6-8 inchs of pipe up from the tee and on top of that he installed the valve. This is leagal in some state you will need to check your local codes to see if you can do it this way. As far as drainage it seams to work great.