[fallard]

My boat originally had a Nauta PVC flexible tank, which was odor-permeable. I have since replaced it with a Nauta tank that is nitrile-lined, after talking with a Nauta rep who mentioned that you should never use a PVC flexible tank--Nauta or otherwise--for your waste tank. The tank I have is also rated for diesel. I have used a similar flexible tank for extra water.

Agree with Minne: get a poly tank if it is cost-effective. The flexible tanks have never failed/leaked, but I would probably be more comfortable with a rigid poly tank that didn't wiggle.