my son drove about 10 miles with less than 1 gallon of diesel? can we drain the tank and fill up with gas to avoid a problem?
Explain your question a little more fully, please.
You can drain the fuel tank if you wish but one gallon of diesel fuel in a 20 gallon tank should be tolerable. Diesel fuel is a better lubricant than gasoline but is less volatile and has a lower octane value. You may not even notice the reduced performance.