Jason,
I would reccomend that you find a PVC connector that will mate to the factory pipe, then add a small piece of PVC to it and a Standard bayonet fitting to the PVC. You could go with a Valterra or if you want to stay Airstream get a Thetford one. Then you have a cappable connection (DOT required) and can eaisly attach a hose.
Was yours a "park model"? It is very possible someone modified yours in past, as I thought all airstreams had a quick disconnect.
