We are installing an island in our kitchen and the first plumber we had told us we did not need a separate vent for the island sink. He told us that connecting the island drain to the main drain and vent would suffice (first picture is what he did). I realize we need a cleanout with the drain, which will be installed after the cabinets.
Now, our new plumber told us we do need to vent the island sink or it "would bubble and have problems draining". However, our new plumber did say he could connect to the vent from the main sink (see picture) which is in the wall (trench already cut in wall to left of window). He told us he would "install an upside "u" with a cleanout for the vent and go back into the floor, through our crawlspace on an upslope and up through the exterior wall to connect the existing vent".
Which is correct? If we need to vent the island, will the upside "u" be the way to go about it? Finally, can we connect to the existing vent?
Our state only has a final inspection on a remodel so we want to have it right before they get here. Thanks!