We're in the middle of an apartment remodel and just set the tub and noticed some popping/gurgling noise coming from the drain. A few days ago the indoor A/C unit leaked around the pan and the plumber removed the existing trap at the unit. Prior to removing the trap, we located the drain line connected to a tee that went to the tub trap. Apparently it's double trapped and either overflowed the other day or leaked enough around the drain pan to cause the carpet to get wet hence the reasoning behind removing the A/C drain line trap but in doing so caused the aforementioned noises. The plumber did fix a small hole in the drain pan so I requested to have the trap reinstalled and after some hesitation and a little arguing it got put back in and all is well again. Is there potential for this drain to back up or would the tub drain at worst just suck the water out of the A/C drain line trap?