I believe you have a 'vane' type of cap that covers the plumbing vent pipe. These are sold as an aftermarket item...I've even seen them at Wal-Mart's RV parts area.
Cyclone Sewer Vent - Camping World
They are supposed to rotate with the wind and cause a small 'suction' or air pressure change that will allow air flow up from your holding tank and vent it 'down wind' no matter which direction you are parked.
I have one on our Lance Camper and it seems to work as advertised. I don't plan to install one on our AS, however, as I like the Alum cap that matches our rig.
Linear Mode
