Inadequate sink venting

[LookSmart]

I often come across gurgling drains in sinks and tubs in bathrooms. Often there is an S-trap installed at the waste pipe (when visible). Is this problem caused by inadequate venting, the S-trap or some other cause. Will a Mechanicle vent cure the issue? How would the tub be vented? I just want to give my home inspection clients the right answer. Thanks.

New Jersey Home Inspections

[resqman]

Is this problem caused by inadequate venting, the S-trap or some other cause. I just want to give my home inspection clients the right answer. Thanks.

New Jersey Home Inspections

Yes, Yes, Potentially. Have the problem corrected by a licensed plumbing contractor.

[Tom Raymond]

The issue is with the venting or with the drain lines (blockage, improper slope, etc.) not with the S trap. In my own house the upstairs bath has no vent, the tub has a P trap and the sink has an S trap. The tub trap occasionally syphons, the sink trap never does.

Tom