Trying to tape up a TLR rim to make it air tight is not a trivial matter. Most of the time you end up with small leaks that can be plugged with the sealant. But sometimes the leak is too big for that. You'll just have to bite the bullet and retape it. The valve hole in particular, is a common place for leaks to start. There are three things you can do:
1. when you make the hole for the valve- make a small hole and push the valve stem through it gently. Don't let it rip.
2. you can also end the tape short of the valve hole. Such that the valve only contacts the aluminum rim, without any tape there
3. tubeless tape, like Stan's, tends to be very stiff and not stretchy at all. It's hard to make this tape follow the contour of the rim bed. Electrical tape is much stretchier and easier to press into the contours of the rim bed. But it's too stretchy to use on its own (tire pressure would push it into the nipple holes). You can, however, use it on top of the tubeless tape where you need to make an airtight seal. Or in a location where it's in no danger of being pushed into a nipple hole, like over the rim joint line.