Our kitchen sink has two 2" ABS drains straight through the floor, where I assume they come together. The basement is finished, so I don't have access below the kitchen floor. The sink is on an island, so there is no way to vent through the roof. The original plumbing used a loop just below countertop level connecting above the two sink drain holes. I assume this was for venting and perhaps antisiphon? I am replacing this plumbing as part of our remodel, and will have to either lower this loop to accommodate deeper sink basins (the new loop would be below the bottom of the basins) or install an air admittance valve at the top of each ABS stack left under the sink (but above where the PVC of each sink drain enters the ABS stack). Which way is best? Or is there another way I should consider?

Does it look like this? This might help. Black & Decker Power Tools (http://www.blackanddecker.com/projectcenter/ProjectDetail.aspx?DOC_ID=p_2_47_15500_15509_15543 .html)

A regular vent's always preferable to a mechanical vent unless it's impossible to run a regular vent. The reason being that mechanical vents can fail. That's why it's against code to cover up a AAV. They must be assessable so they can be replaced. Good luck, Tom

Our kitchen sink has two 2" ABS drains straight thru the floor, where I assume they come together. The basement is finished, so I don't have access below the kitchen floor. The sink is on an island, so there is no way to vent through the roof. The original plumbing used a loop just below countertop level connecting above the two sink drain holes. I assume this was for venting and perhaps antisiphon? I am replacing this plumbing as part of our remodel, and will have to either lower this loop to accomodate deeper sink basins (the new loop would be below the bottom of the basins) or install an air admittance valve at the top of each ABS stack left under the sink (but above where the PVC of each sink drain enters the ABS stack). Which way is best? Or is there another way I should consider?
If the current system is a foot vent, I'd cut and cap the 1-1/2" vent and just install an AAV, provided your local authority allows AAV's, of course.

Does it look like this? This might help. Black & Decker Power Tools (http://www.blackanddecker.com/projectcenter/ProjectDetail.aspx?DOC_ID=p_2_47_15500_15509_15543 .html)

Nice photo illustration of a foot vent, but it wouldn't pass inspection as is -- It needs a clean-out on the vertical portion of the vent coming up the wall -- And the two sanitary tee's below the floor should be combo's.

Also, the 2" clean out below the floor would be great if installed where accessible from a crawlspace, but would be useless if there is a finished basement below it -- In that case, one would need to install a clean out tee just below the trap arm tee.

Yeah... missing a cleanout. I found a better one.