people have run crazier fuels, i wouldn't be surprised if it worked OK.

sveinn, where is your information on underground tanks from?
the rules i found sound reasonable:

http://www.waterboards.ca.gov/water_issues/programs/ust/docs/biodiesel_regulations%20letter_1_20080229.pdf

Clarification of Regulations Applying to Biodiesel-E Stored in Underground Storage Tank Systems (PDF) Exit EPA Disclaimer (3 pp, 44K, About PDF)
Prepared by the California State Water Resources Control Board, this memorandum clarifies state regulations pertaining to storing biodiesel in USTs.

__________________
'77 240D, 504H, OM617.952, etc.