Chaan

Issue: My bathtub waste pipe drains only when plunged, despite confirming there are no blockages downstream (snaked the line and visually inspected accessible sections). The problem persists even after clearing the P-trap and nearby pipe segments. Proposed Solutions: Air Admittance Valve (AAV): Suggested as a fix to address suspected venting issues causing negative pressure/airlock. Anti-Siphon Waste Pipe on Connected Sink: Another plumber recommended installing an anti-siphon device on the sink (connected to the same drain line) to resolve the bathtub’s drainage problem. Could I please request for Expert Insight? Would the anti-siphon waste pipe on the sink effectively resolve the bathtub’s venting issue? If not, why might this solution fail? I’m aware anti-siphon devices are typically for backflow prevention, but the plumber claims it could act as a vent. Is an AAV still the more reliable solution? Thank you for your guidance on prioritizing these solutions or suggesting alternatives.