Quote: Are you using the vacuum to pressurize the tank (help push the dent out) or to, hopefully, evacuate potentially explosive fumes?
Also, I'm wondering why you want to segregate winter diesel from summer diesel?
Even though pure grade no. 1 diesel fuel may seem an excellent solution due to its low gelling point, it's more expensive and has a lower energy content. Running an engine on pure grade no.1 diesel fuel continuously could reduce the fuel system's life (Lifted from an online site), + I think it might contribute to more cylinder wash down=oil dilution, especially on a high hr engine. Fuel will likely never be cheaper than it is now, so the more on hand the cheaper overall. On the vacuum yes, out with the bad air, in with the good air, though diesel fuel I don't worry about too much, gasoline is a whole different thing. Mike