Looking for a Harbor Freight Pump Gas Cap

[Travelover]

maybe a 2-1/4 npt black iron pipe fitting ? or plastic/pvc npt fitting?
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or even brass my bus uses one about 2-3" in dia

Ding, ding! We have a winner. Turns out it is a 2" NPT thread. I found a PVC cap that screws right on. Now I need to cobble some kind of gasket and make a little vent hole