You can wash the tanker (I assume it's a large trailer) by hand with a pressure washer. Just be sure to use the right stuff when you wash.
On occation i've been known to milk cows for some people I know, and they use a non foaming "milk soap" and an acid rinse to clean their lines and storage tank. The dairy industry is very strict about bacteria counts in milk, so this stuff must come pretty close to killing almost everything without killing us.
just an idea.