As noted, sugar is not soluble in gasoline, so putting granulated sugar in the tank does nothing more than clog the filter. If a fine enough powder sugar was used that could make it through the filter (I don't know if powdered sugar is fine enough to do this), then it could possibly get into the injectors and clog them as any dust would do.
I'm not certain, but I'd suspect that any sugar that made it into the cylinder would be consumed during combustion, at worst leaving behind a "varnish" like coating.
If the tank was instead contaminated with antifreeze, then you have a different type of problem. Of course the first thing to do is empty and clean the tank. I'm not any kind of expert on how to handle this, I think it could be done without removing the tank through the gasoline fill port. Antifreeze contains substances that could harm the engine, so flushing the tank to remove any antifreeze would be very useful. Antifreeze is water soluble, so part of the cleaning process can be done with distilled water, which is relatively inexpensive. However, you'll also need to remove any water left, which can be done with methanol and still burn cleanly with some water in it.
I'd first siphon out the fuel completely, then flush any remaining coolant with a few gallons of distilled water. Then with the tank as empy as possible, I'd flush it one more time with < 1 gallon of methanol to dissolve any remaining water. I'd run some of the methanol out through the fuel pump, without the fuel filter and into a container to flush that as well.
Once the flush is complete, a gallon of gasoline can be used to flush out the remaining methanol. Although a small amout of methanol mixed with gasoline will not be a problem for the engine, it would be worth flushing this out once more to remove any remaining coolant residue from the tank.