Kelson,
I test a few different ways. I built a swim tank with a recirc pump, take a few out every time I'm out in the boat, I also have access to 6 very large artificial streams here at work that I can toss them into. Right now I'm in the process of building a swim chamber that is made from clear PVC piping that I'll have a dc motor coupled to a pump end with an adjustable speed control. Still have not verified the derby, but at this point, it really doesn't matter to me. I've been busy enough as it is.
Rob