Were putting in a diesel motor in our boat and am for the most part using the existing exhaust setup, but need to add some exhaust pipe to connect to the existing. The motor has 1 1/4" female thread to hook into. This part of the exhaust will be all dry so plan to use metal pipe, but what kind of metal? We are in fresh water, if that matters. The motor is a Universal M25xp, so it has a heat exchange for engine cooling.