Just make sure you're washing with cold water, if the water is two hot it will remove a lot of you dye. As for the sink clogging that really does have more to do with the wig you've purchased over the dye.
Also in regards to using a tray over a spray bottle I wouldn't recommend it, just use a funnel to get the alcohol into your spray bottle, that way you won't have to worry about missing it.
I've hidden my phone humber somewhere in my cosplay gallery. If you find it you can call ^_^. J/K or am I.......you'd better check........