I have noticed this event at a couple of newer homes built in the 2000’s.
When the stopper in the sink is released and the sink has water in it air bubbles are escaping. Drainage is ok but not great, the bathtub does not have the same issue, both are vent with the same stack, the house was built in the late 60’s.

Once the water begins to drain the bubbling stops and no girgling sound is heard once the sink has emptied.

Had this same senrio awhile back in a remodeled house from the 60’s. In the master bath, shower drained fine, sink did the bubbling then drained out a bit slow. Wrote up as such suggested that it could be a venting issue or a partially clogged drain line and ref. to contact a plumber.


As described in the OP, this is not an issue. There is a quantity of air between the water trap and the water in the basin which must escape as the basin drains into the tailpiece. Water is trying to go down all at once and air is trying to come up all at once which effectively slows the drainage. Once that air escapes up through the basin of water, regular drainage is occurring just as the OP stated.