Originally Posted by
Kontact
To correctly tighten valve in rim, use a hard object to push the valve in from the tire side, compressing the rubber seal. While applying pressure, handtighten the lockring.
I agree with this completely, and have done so many of these tubeless valve stem installations at my shop it's a muscle memory thing for me. The only possible variation I'll add is that I use my thumb as the "hard object."
When it comes to creating an air tight seal, just remember, it's not the presta nut on the outside of the rim that's creating the seal, it's the rubber base of the valve stem on the other side of the rim that's creating the seal. The key is pushing that rubber grommet/seal FIRMLY "into" the valve hole by whatever means; the presta nut is tightened to hold that seal in place, and it will, if you do it correctly.