In Limit poker it is not easy to isolate someone - sometimes the marginal hands you play against a maniac you eventualy lose to a legit third party.
I think the way to handle it is position instead - specially in 5-draw. Whenever you act after the maniac you have a strong advantage and you can profit - folding or re-raising. Leave one guy between you and him and take all his money on the long run. Leave and re-join the table if possible to take a better seat.

This is also valid in Pot Limit - but it is easier to isolate or get out when another player shows he is strong and willing to chase the maniac.