Chris...just sink or hit a light oil barge where there is a lot of tidal current.
Never hit something with asphalt or crude.
Other than that...out of hundreds of salvages..I don't think I have ever heard of "environmental cleanup" charged other than a few oil diapers and a couple man hours of labor. The other way is a pump out of the sunken vessel if the USCG determines the fuel or oil left onboard is an environmental threat.
Probably why the insurance companies have been raising the limits so much and not really charging that much more. They just raised mine to $800,000, no additional charge.