Ultrasonic cleaner solvent?

[MThuntr]

What type of solvent are guys using in ultrasonic cleaners?

For context, this will be for filthy 22lr suppressors, assorted gun parts, etc but it may see a carburetor and other small engine parts. Would it be smart to have 2 different solvents for guns parts vs engine parts?

 

[p_ham]

4:1 water and Simple Green for everything but aluminum.
I use Simple Green Extreme for AL.