You don't need to be under there with it running. Just clean it up real good and then run it for however long you think it needs to to develop a leak. Then shut it off, give it a few minutes, then take a look. Use a small mirror and a flashlight if you have too. If you are having trouble seeing, try getting somebody to help you out that can.
The dye and blacklight penlight are what I used on my truck when I was having some leak issues. I want to say the light was $12 and the dye was $6 from Carquest. The dye isn't real bright, so you don't really want to be checking it out in bright sunlight, for example.
