Here is the culprit...the drain pipe that is to low to meet code. Apparently the s trap is not allowed these days...come on! It's retro! So 1920's.... Anyway, when the plumber said we would have to take out the sink cabinet...which was built in with a single face frame for the whole bank...which was already sprayed gray ...I said that's not really an option. Luckily we could remove the back of the cabinet and pull away the rosin paper, and it should be accessible enough. I taped the face frame to protect Brent's spray job.
We were super lucky that the plumber was able to come the next morning AND get the inspector here by lunch. But ... replacing the drain pipe was an ADDITIONAL, significant cost. I'm beginning to think I should have married a plumber :)
The final work looks great. We passed inspection and so can finish the drywalling today (all behind cabinets, so no biggie). ONWARD, HO!