Water building up in bathroom sink, starts to drain then air pops and drains very quickly, what adjustment do I need.

Sounds like a plugged vent in the system. Is there an AAV on the sink?

Hi CRMACKIE

Does this sink have anoverflow hole? If the sink does have an overflow hole then you may want to try adjusting the pop-up to pop up a little higher when the lift rod is pressed down... that will allow more air to mix with the water draining. If the sink does not have an overflow hole then you will be best off installing a mushroom style vessel sink drain in the sink (see image). Here, without an overflow hole there is little air mixing with the water as the water drains into the drain... a mushroom style vessel sink drain has a push button design that forces water to flow over the top of the drain and cascade down the umbrella-shaped dome and mix with air before entering the drain. Mushroom type vessel sink drains are available at all home improvement stores nowadays.

Attachment 49087

Back to you...

Mark