Let me correct my statement, and I will go back and edit my original mistake. If there is a sanitary tee in the wall there, then the venting would already be ok. So no change from what you did would be needed. Sorry. I was not thinking.
Thank you, Reach4! I don't think my old plumbing had an AAV, but it seems like a good (meaning effective and easy!) solution. I wonder if this is why my old sink always drained slowly.
Lack of venting does not cause slow draining of a sink, at least not as a single problem. Instead bad venting can cause odors. Partially clogged pipes cause slow draining. Kitchen drain pipes clogging where they turn from from vertical to horizontal, maybe under the floor, is pretty common. If you have slow draining, somebody should snake the line down through that top port or remove your trap, and snake down from there.
I got a RIDGID PowerSpin Plus.
I powered it with a drill.
I bought it for a lavatory drain, and it worked great for me. I actually went through the 1-1/4 trap, and before I knew it, it had played out about 12 ft of snake, and the blockage several feet below the santee had been cleared. I was prepared to enter at the trap adapter on the santee, but thought I would try the lazy stay-dry top entry. I know it has limitations.
If you entered the top port, and aimed down, you could run water while the snake is going. Just don't run water fast enough to leak much out of the port you are snaking through.
Or have somebody do this for you with a bigger snake. A hand snake may just push a small hole thru a clog, and the clog may not be taken out.