Another type of vent is the anti-siphon trap vent device. These are used as a secondary vent to aid in draining sink fixtures. Also called “check vents,” ASTVDs allow air into the drainage system, but prohibit air from passing out of the system. ASTVDs are installed in the liquid drain piping system, at or near a P-trap inside a cabinet. Look under the kitchen and lavatory sink area and you should find them.
They sometimes go bad.
The rubber membrane used in ASTVDs can sometimes dry out and become stuck in the open position. If holding tank odors are bad under a galley or lavatory cabinet near the P-trap, chances are it’s time to lubricate the rubber seal inside the ASTVD. Use Dow 111 lubricant to moisten the rubber diaphragm. Since it is located above the actual flow of waste water, the ASTVD is simply threaded into a fitting above the trap arm and is usually easily removed for inspection and occasional lubrication.
Mark & Susan
'13 Cruiser Patriot 335SS - '13 Ford F150 SCREW - PullRite Superslide - Roadmaster Active Suspension
Member - "Northeast Adventures RV Rally Group" & "Mason-Dixon Bunch"