It would help if I knew what it is, you've left it way too vague.
Is it something that is going to make the chin sick if it eat it? Or something that has hardened? If so your best option is to just clip the furs off. They will grow back, but the tail fur does take longer to grow. If you don't know what it is I would go with just cutting it out, better to be safe.
If it's something that isn't going to make him sick, try combing it out. You can use a damp cloth to try to loosen/re-moisturize enough to get the comb though. Make sure to dry the tail off when done and then give a dust bath. If it's still sticky you can try rubbing dust into it to hopefully stick to it and give you something more solid to be able to comb it all out.