I've had a aux fuel tank (100+ gallons) in my PUs for the last 50 years. While it mainly has diesel in it, I put gas in it too. When switching I park so the tank's pickup is on the low side so I get most of the fuel out of the tank and then put in the other fuel. While the above post is correct about it being Kerosene, I've used gas in my summer diesel during the winter.
OP, doubt you have a hose long enough to reach your truck, but I'd do it and not worry about the little bit of gas in the diesel on the first tank... just get as much as possible out of it first. For the Nay Sayers you could put a couple gallons of diesel in first and then pump it out and save for starting fires... treating this mixture like it's gas when lighting it.