If you put Gasoline in your Diesel Pickup by mistake, this is what I did to prevent major engine damage. I did not have to drain the fuel tank, and it cost less than $40.00 to cure the problem.
I had an 03 Dodge with a 5.9 Cummins Diesel. The factory tank held about 35 gallons and my saddle tank held about 42 gallons, about 77 gallons total. I had maybe 5 gallons of diesel in the truck when I started to fill up. After I'd put 20 gallons of gasoline in, I realized my mistake. At that point I put in 4 or 5 qts of motor oil and finished topping off the tank with diesel. Approximately 25% of my capacity was gasoline.
My pickup started right up and I drove 10 miles to Walmart to buy more motor oil. I think I added 3 or 4 more quarts of oil to the diesel tank. When I tried to start it, it would not start.
I removed the Fuel Filter and filled the canister with standard Transmission Fluid, put the Fuel Filter back on and it started right up. I had to make a 300 mile trip the next day pulling a trailer, so every 60 miles or so, I topped off the tank with diesel for the entire 600 mile round trip, and I continued to top off the tank every 60 miles for a week or so. I put a new fuel filter on at the end of my trip and changed it again three weeks later. After that, and every time I put in 30 to 35 gallons of diesel, I added a quart of Transmission Fluid for 3 or 4 months. It took a few months before it finally quit smoking, which was not much to begin with.
Maybe I was lucky, I don't know - but I've put well over 150,000 miles on my truck since then with no problems.
If you have a similar story, we'd love to hear about it. email@example.com