I have Perrin turbo inlet which is 2.75 inches internal diameter.
I went to Lowe's Home Improvement store to purchase it all, but I'm sure Home Depot or any Hardware store would have it.
Sku# 23306 - 2" DWV Plug MIPT
Sku# 23302 - 2" Cleanout F adapter
Sku# 23360 - 2" Long sweep Elbow
Tire valve stem at Pep Boys
Cement glue and silicone
I glued the DWV into the elbow
Then I dremmeled a hole for the valve into the cleanout adapter.
The valve stem pressure fits and seats into a groove (kinda like a snap-grommet)
Then I put cement glue around the stem just for added strength
Then after it is totally dry, I smeared a generous amount of silicone around it.
Screw the cleanout into the DWV plug, and use a wrench to really tighten that sucker down.
Then I stuck the whole piece into the Turbo inlet and clamped the heck out of it.
I also plugged the 3 ventilation ports on the top of my inlet.
Ran about 10psi through it at first and didn't notice anything. Then I turned it up around 20-25 psi and found the leaks immediately. Fixed the leaks by adjusting pipe and retightening. Did another test and no leaks. Car started up with NO rough idle as it had before.