and if so, how do i screw this thing in and know its making a good seal?

Longass rubber hose ...

 

The o-ring will make a good enough seal. My compression tester has the same type of setup. Make sure you have the right fitting for you spark plug hole (IIRC, M14x1.25).

 

looks like a nice piece...you can if you want put a little vaseline on the o-ring to make sure she seats nicely and not dry other than that just screw her in(dont forget to take out your fuel pump fuse)

 

thanks for the replies guys, my main concern was if hand tightening it would be good enough.

 

Yeah, I have that same type of tester and hand tightening it always works fine.

 

Make SURE that all the fittings on the end of the hose are tight. I have had them come apart when they're down in the sparkplug well. It was unpleasant to get them out.

Also the more hose between the head and the valve/gage will yield a lower pressure since the volume of the hose will be like adding volume to the combustion chamber. Shorter hoses will be more accurate.