Proper tubeless valves can have issues that the rubber doesn't always seat properly in some rims. May require some bodging maybe to fashion a rubber seal inside. The outside needs a rubber seal also really.
Or ghetto valves - simple cut one out of an old tube and leave enough rubber for the inside to make a seal and then use a o-ring on the outside or make one from spare bit of tube rubber.
Either way you *must* chuck in sealant. Lots of sealant. Big tyres, 2.35 for example, 2 or 3 cups, maybe even 4. Especially if the tyres are tubeless ready or even "not technically ready but are really" (i.e. regular Maxxis Minions, HR, etc), and definitely if you plan to run low pressure (sub 30 psi). UST tyres may need less sealant and technically you can use none but I'd stick in loads anyway. You need something to seal small punctures as you ride and it does help keep the bead and valve hole sealed.
Sealant - Stans. End of.