This is a new one for me. The P-trap is attached properly but the drain loop above it is attached to the top where the vent should be and the bottom just below the p-trap. I thought it may be a way of stoping syphoning but really have no clue. Any help would be appreciated. Sorry It the only picture I have.
Island sink?
Yup!
It may be an attempt at this… but doesn’t look to extend high enough. If drainage was fully functional after observing a full basin of water drain with no burping, I would note it as ‘not installed in accordance with best industry practice but drainage functional at time of inspection’.
This could be the answer. It did burp when I filled the sink and drained it. You could here it trying to suck air from the overflow. I could almost stop it completly when I put my hand over the overflow. I wrote it up as needing to be evaluated and repaired by plumber.