Most of the sewer hose connectors are Valterra. Airstream and Newell, as well as a few others used Thetford fittings. It is not nearly as easy to find Thetford fittings as Valterra fittings. The old hands would certainly know about Thetford fittings but the newer sales people might not.
Camping World sells the Thetford sewer hose fittings
http://www.campingworld.com/shopping...-fittings/4182 as well as mail order companies like RVParts Center
http://www.rvpartscenter.com/prodsel...DID=10&CID=414 . Valterra sells a Thetford to Valterra adapter that allow you to connect a 'standard' Valterra sewer hose connector to a Thetford fitting:
http://www.valterra.com/RV/valve_caps_and_adapters.htm (bottom of page). The Thetford connectors are more durable but harder to find.