Sewer Gas Problem - How do I fix this?

Believe it or not, this is not a DIY job. Or at least not entirely. We had a single vanity converted to a double several years ago by a plumber. When we re-did a couple of months ago, I simply re-connected everything as is. With the old vanity I didn't have any problems with the drain on the right syphoning out the trap on the left, but now I do. I'm not sure if I created the problem by increasing the pitch, or what - but now I need to fix it.



It attaches to the drain pipe in the wall with a threaded male fitting, if that matters.

You should not have a sewer gas smell. Is either of the traps dry?

Some places do not allow this set up.... Here we would the sinks joined with a tee and one trap with outlet to the wall. Other places would require two traps with separate connections at the wall. But this should not siphon a trap.....I would look for another source of odor.

The trap in the left sink was dry and that is where the odor came from. As soon as I ran a bit of water into it, the smell went away. It's happened a few times now. For the time being, we make sure that we run a bit of water into the drain on the left if we have used the sink on the right. So I'm guessing that siphoning is the problem. I could buy and install one of these:

If I understand correctly, they would just fit onto the sink tailpieces. Then I could attach this P-trap to the horizontal part of the fitting above:


Assuming I've got it correct so far, how do I attach that trap to the female fitting at the wall? Is there an angled fitting I can use? Also, I have black ABS there now. Should I continue to use it or should I be using PVC? Does it make any difference?