In a rinsed out 2 liter soda bottle, mix:

5 cups water
1 cup stove alcohol (denatured works, too)
1/2 cup ammonia (I use Parson's Sudsy)
2 tablespoons detergent (NOT soap)

I put this in a little spray bottle (from used-up CA Activator for example) and top it off after each trip to the field. Some folks here say ammonia makes Monokote brittle, but I haven't noticed it and this formula is used by lots of folks in our 90 member club.