During my framing inspection, the building inspector thought I would need a 2 inch sink vent. Here is the layout; double sink has a 2 foot long 1 1/2 trap arm with a dishwasher connection, drains into a 2 inch pipe that is 22 feet long going into the 3 inch main house drain. I was visualizing an 1 1/2 vent pipe at the sink end of the 2 inch drain pipe encased in the outside wall so I drilled a hole for this size pipe within the wall construction. Could the plumber be installing a 2 inch vent pipe up through the roof ?? I did not want to ruffle the feathers of the Building inspector as really he should MYOB it's not his department.