This isn’t totally helpful because it gives you more possibilities, but air coming out by the valve doesn’t mean the valve’s leaking- if air leaks into the rim anywhere, the easiest place for it to escape is usually the valve hole as nipples seal up their eyelets pretty well. So it could be you’re looking in the wrong place.
IMO the best way is to keep it simple- one layer tape, cut very cleanly (super sharp scalpel is my favourite way, there’s others, what matters is just that you get a perfect hole. And the best valves I’ve used are these:
http://www.superstarcomponents.com/en/alloy-tubeless-valve.htm
The taper tybe valves are much more forgiving ime, and these are bigger and squishier than Stans so work even better- I had a set of stans rims that some monkey had drilled out for rim strips, incredibly badly, and these still sealed them up- didn’t really believe it’d work.
There’s tons of bodges but if the parts are decent then doing it right should work, better than anything else.