Just a quick heads up.
The fresh water and holding tank deck caps on my boat #174 were made by Wilcox & Crittenden. Do not drop one overboard!
The thread for these caps is proprietary, and to the best of my knowledge are unavailable. I got lucky, found one at a boat yard in a used parts pile.
Otherwise I was looking at a new hose, deck fitting and about 15 hours of labor.
BobG