What the successful landlords use to ventilate housing. You call them PVC Elbow Vent and Plugs. We call them 3/4" Sch 40 PVC 90 Street Elbow - Mipt x Fipt and matching 3/4" Sch 40 PVC Plug Mipt. But basically that just means the elbow has exposed threads on one side for easy insertion in a 3/4 inch hole drilled into the side of your gourd, gourd cap, or housing and the other end has internal threads to accept the threaded plug that lets you cap the vent when the weather is still cold outside. It's a win win.
Sold in one set. That's 1 elbow and 1 plug.