I'm sorry to hear about your experience. I've been felting clothing for awhile now and I've not had this experience. I don't really understand what you mean by the wool came out in clumps. What type of coat was it? When I've disassembled clothing I never do anything to the edges. In my experience I only have had to do one wash and hot dry as the fabric has nothing stopping the felting process.
I'm very curious and concerned as I am on septic and I do not ever want to have to have that replaced again (just did that about 4 years ago. Not fun!).