Actually I'd be a lot more worried about some water-based soapy concentrate going through my fuel filters, injection pump, injectors, and engine than the guy who put a few gallons of gasoline in his tank rather than diesel. In that case they towed the car, then drained and flushed the tank and everything.

The alcohol trick may work; something like drygas or the cheapest fuel additives, or gas line de-icers, are mostly alcohol. I'd probably go with a fairly large amount of it, maybe starting with two bottles, and adding one every time drove the car, figuring a fairly full tank wouldn't mix as well with stuff on the bottom as an almost-empty tank.

I wouldn't be crazy about running a soapy emulsion of car wash concentrate through my engine, but I'd be even more worried about the concentrate killing my engine at speed.

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic