Well I went looking in my garage and I stumbled on a bottle cap and a 1/4 npt fitting. The cap looked the right size so I tried it and it seemed to fit well.
So I drilled it out with one of the step drills and then decided to use two rubber washers.
I could not find a bolt to fit but tomorrow Ace/Princess Auto has one. Now I think it should hold simply by compression and I should not need any silicone or other sealant since according to Motive the kit is pressurized to only 10psi if it does I could always seal it.
What say you heir Gordo.