You probably have a Thetford connector. That would have been one of the last years they used them, I would think. There are 3 things you can do:
1) You can get an adapter to couple the valve to a now-standard Valterra fitting.
2) You can make a hose with a Thetford end on it so that no adapter is necessary
3) You can update the plumbing on your trailer, replacing sufficient components to end up with a Valterra fitting.
The pros and cons of each are pretty clear. vintagetrailersupply.com has parts for all alternatives as do most Airstream dealers and better RV service shops that work on older rigs.
Camping World and similar places may have the adapter (look for a "Thetford adapter") but typically will not have hose ends.
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