I did the very same thing at a Flying J in Wells, NV. They syphoned as much out of the tank & put in 5 gal diesel & 1 gal 30 weight non detergent oil & drove to the fuel island where I refilled tank with diesel. He gave me another gal of oil & had me put it in the next fill up. Never had a problem. It was on my 92 Ram. He only charged me $60. 00. Just Like Bob said.