Decal setting solution does the same thing as detergent, but a bit better. If you are out of setting solution, or real cheap, a tiny drop of detergent in water is an alternative, but I still believe the setting solution is better.
Vinegar is another alternative. But, you must ensure that the vinegar does not have any particulates that will end up as residue. Many vinegars add spices and such, which we don't want on the model. Some good white vinegars work well, but I still prefer the hobby shop stuff.
Any old photographers getting rid of their darkroom stash should save wetting agent packages. Mix it a bit more dilute than you did for printing- it is the same stuff as the setting solutions.