We use 2 types of fog juice at our shows in our heat foggers (like these) - Froggy's Swamp Juice (
www.froggysfog.com) or Martin I-fog (
www.centerstagelighting.com) - they're formulated to have higher volume output (about 6-10X that of the cheapie juice that comes with the foggers) and far longer hang time, as well as almost NO residual (which the band members and singers like a whole lot!) PLUS they don't plug up the fogger like the shit they give you with the unit.
If you're not going to use the fogger for more than a week or two, you NEED to clean it, especially with the crappy juice, or it will plug up and fry on you (trust me) - I use a 1 part white vinegar to 3 parts distilled water solution, empty the tank and pour in the solution, run about 4-6 20 second bursts (OUTSIDE, unless you like the smell of burning douche) then rinse the tank thoroughly with distilled water, refill it with distilled water, and run another 4-6 bursts until you can no longer smell the vinegar. Lastly, empty the tank and put some fog juice in it, and run a single short burst until you just get fog again, then store it (leaving the lines empty is almost as bad as leaving them full, you want a little juice in there but not enough to have the pump and lines full).
Seriously, guys - try a gallon of the Froggy's Swamp Juice, it's only like $30 shipped and will last you basically forever with a smaller (under 1500w) fogger, plus you won't funk up your room or your lungs!