FYI: I am in the process of trying to replace a defective donut in my '95 Jayco 1206 pop-up. I called the local RV store here in Central Coast California. They called Jayco and found the part was no longer available. I am looking for a half inch piece of rubber or foam rubber to try making a new one. If that doesn't work, I think I'll find a way to modify the drain as described above. I found the part in the Jayco Catalog. I'm attaching a screenshot. Also note: the specs appear to be inches. 2.75" OD, 1/2" ID, .63" Thickness.