A member at a club I used to belong with came up with this formula:

<span class="msg"><font size="2">"Jim Quinn's Mix"

5 cups water
1 cup alcohol (91% isopropyl or stove alcohol)
1/2 cup ammonia
2 tsp detergent

I carry a little two ounce spray bottle in my flight box (a recycled CA accelerator bottle). I refill from a two liter plastic bottle.  I have used this for more than a decade on gas and glow models with no ill effects.  I use Parson's Sudsy Household Ammonia and Dawn detergent.</font></span>