Stainless Steel. Steel and Aluminum can be OK, too. Certain plastics are proof against such aggressive hydrocarbons, such as PE and PP. PVC is not one of them, including CPVC.
Go to
http://mbca.cartama.net and search their forum, there are several posts on biodiesel, including some web references.
Finally, note that SVO (straight vegetable oil), WVO (waste vegetable oil) and Home-made biodiesel all cause damage to varying degrees to all diesel engines. Only Biodiesel meeting the published ASTM standards is OK for most engines.
Very new (MY 2007 and later) passenger cars equipped with diesel engines require the use of ULSD (Ultra Low Sulphur Diesel), and most manufacturers state that anything more than B5 (5% Biodiesel with 95% conventional diesel) is not acceptable, as it causes irreparable damage to the emissions control system. (Kinda like leaded gasoline when catalytic converters first came out - but you wouldn't be old enough to remember that...)
Don