Did this very thing this summer:
Wife put almost 6 gallons in ours. She noticed she had grabbed the wrong nozzle stopped the pump and called me. We were headed out of town and I was at the parts house getting plugs for our jet ski's. I picked up a bottle of Marvel Myster Oil and a bottle of Power Service. Poured them in and finished filling it up. Hoping to do what
bugnout described above. After about 40 miles it started acting up (high rpm's, lossing power, loosing speed, problems pulling hills). When we got to the lake I left it at the storage facility and called the dealer. Long story short called brother-in-law and had him bring his trailer so I could carry it to the dealer. 3 days and $600.00 later it was fixed and running great. They dropped the tank, dumped it, flushed it, flushed lines, changed fuel filter, and performed injector service.
I asked about siphoning the tank to drop the mixture and found out that most vehicles have a valve in fill nozzle where it can not be siphoned.
It was not totally her fault it was a new station and every handle on every pump had a green handle. The next week they changed the handles and only green handles were diesel. I talked to them about the problems the following week and of course they denied any responsibility. A lawyer would have cost me more than the case was worth so I let it drop.
Later thought about buying some 5 gallon cans put it on a lift open the fuel line somewhere and turning it on and let the pump empty the tank. Filling the tank and changing the filter and going for it. Any thoughts on this.
Also Insurance reimbursed us for the issue on comprehensive policy, except for deductible.
I have done the same thing with my Dodge Cummins but it was only about 2 gallons and a 34 gallon tank. No problems.