late post I know but I clean my epoxy brushes in denatured alcohol, once they are apparently clear of epoxy I wash them with dawn and warm water. I have been doing this for years with no problems. About your ruined plugs just wet sand them down so they are smooth. You do not need to remove all the old epoxy just get the surface even toned and apply some fresh epoxy. You might want to try Z-poxy brand 30 minute epoxy it lasts a good 20 minute before it becomes unworkable. Hope this helps!
Dean