Wow, glad you have something that works. Weird, advantage did not work on my dogs. Makes me wonder if different regions have different type of fleas.
We had fleas. A friend was training a service puppy. She brought it to our house for a visit from her farm....hence fleas. Our service dogs are very allergic to them. They went to the groomer for special baths and we had an exterminator come out and spray inside and out. We always do it ourselves, well hubby does, but the girls had such bad skin reactions the vet was worried. Fleas were dead by end of day inside, outside I am not sure but we were happy with the spraying. The girls were on antibiotics for several weeks from the skin sores, even though we saw no active fleas after the day of spraying, their reaction to the fleas was horrible. We have our girls on heart worm/flea pills all the time because they go with us everywhere, so we were so surprised to see fleas. This was the first time in over 10 years we had fleas. I agree there must be different varieties of fleas. It was worth the money to have someone spray, it was a one time spray. He would comeback if needed but the exterminator said usually a one time application kills them...it did.
The oil drop on the back of the neck almost killed our kitty, he collapsed in front of me. He was allergic to that flea application, which was vet recommended....just a strange thing. He got washed in Da-n
Dish soap, blue colored one.(did not knew if I can use brand names here, so add the w in the place of the -). We had to wash him three times to remove the stuff, he survived.
What a real mess. I feel for you. If all the suggestions fail, try calling some exterminators and get pice quotes...it may be as expensive after you try so many other products.
Good luck...