you only need a few drops of dish soap as it's only to break the surface tension of the water to stop the little buggers walking on the top of it.
I think they call it a wetting agent, I have a mate who always submerges his clones in this solution for about 20 minutes before transplanting and just gives the plants a spraying with it weekly to catch any eggs that hatch that may have been left. I hope you kill 'em all:thumbsup: