the reason the blaster didn't work is you need somebody to cover and hold a rag over the overflow.
i used to have trouble with opening the tub drains until i started using a snake running it down the overflow.and also i found that this one snake that we have(which has a broken cable)broken meaning the head broke off so it's just a straight 5/16 cable works best because it makes it through the trap everytime.
just in case the coat hanger doesn't get it.