Add UV dye to AC

Got a question about adding the liquid dye to a AC system to help find a leak.

I've seen a video where somebody removed the low pressure schrader valve and used a small funnel to add an 1oz or so of dye.

Using this method It would seem to mean that you would now have to pull a vacuum before adding your R134a. Because you have the system open to air.

So, my question wirh this method is. Would pulling the vacuum not just pull out all or most of the dye you just put in?

I know there are other options such as presurized cans of dye like the Red Tek stuff and also some pricy dye injectors which I assume you can use to add liquid dye to a pressurized ac system.

But wondering what others have done.