if you're gonna do brass make sure you use a solution designed for brass specifically. it'll make sure nothing bad chemically happens during the cleaning process.
i haven't done any ultrasonic yet for brass, just use it for parts right now, but that's because i already have a rotary wet tumbler setup.
i know products like the hornady brass cleaning solution may seem expensive, but once you get into the dilution factor and realize how much actual cleaning solution you can get from a quart, it looks quite a bit more reasonable
hornady for example, mixes out at 40:1 so a quart of concentrate makes 10 gallons of cleaning solution for you.
it also appears that the same mix of lemi-shine and dawn that i use in my rotary tumbler could be very workable solution, but again i havent tried it yet. Maybe i'll give it a whirl with a small batch of brass - i've got about 60 450 bushmaster cases that need cleaning.