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New sink drains fine for a few minutes but then backs up
My brother-in-law gutted our bathroom and re-arranged some plumbing so we could move the location of the tub, toilet, and sink. Tub and toilet work fine, but the sink backs up and drains VERY slowly after running water down the drain for a few minutes. When I pulled the trap off of the tailpiece to see what was going on, some water popped out like there was some sort of suction going on or pressure coming from further down the drain.
The attached image is the only one I have before walls went up. The vent and drain shown here meet up with the tub vent and drain behind those shelves on the right side of the screen. Like I said, tub and toilet have not given us any problems. Is there not enough slope in this vent? Is it too far from the vertical portion of the vent?
What else could cause it to back up and drain VERY slowly after draining fine for several minutes?