Vent stack is probably blocked. Or possibly not connected in the first place, if somebody did a lousy job with the plumbing. Basically, the sewer line should b

Vent stack is probably blocked. Or possibly not connected in the first place, if somebody did a lousy job with the plumbing. Basically, the sewer line should be vented to air on top of the building somewhere, or in some cases air could be let in via an air admittance valve. This should prevent the creation of a vacuum that would cause gurgling or odors.