The tar could not be removed without the help of chemicals which I would not to have soaked into my porous sandals.
So I trashed them. I know...tragic, right? I do take some comfort in knowing that I got them on the cheap from the thrift store. At least I'm not out a bunch of money. I think this might be my last foray into the world of used footwear though. These sandals were pretty cherry though. I could have gotten a lot more use out of them, but they served their purpose I suppose.