I finally got around to putting this together and bleeding the brakes this weekend.
I actually ordered a hose coupling from China to go with the cap, but they sent me an expensive 4 way solenoid valve instead. 🙄 And when the coupling finally arrived, it did not fit because the sprayer uses non standard hose. So I made up a fitting on the 3d printer, and it worked rather well. No need for a hose clamp at 15PSI (about 35 pumps).