When i moved in there was a 5.5 inch top mount sink-this just would not do i changed to a 8.5 or 9 in top mount sink and upgraded the garbage disposal, well i made do with an extended p trap and just dealt with the occasional smell and cleaning the sink pipes once a year to fix it. fast forward. now i just had granite put in and a under mount sink, well now my problem is compounded. The only thing i can think of is going into the wall and lowering the drain pipe. I have to cut the drywall out on an attaching wall to get to the pipe, i am hoping that it goes into the slab, i can not see anywhere else it would go. I am open to suggestions