I have a Whizzinator and some 3 oz. bottles that I practice with as well. I prefer the Whizz, it has been better a maintaining a temperature for me. Another reason is that it is pretty stealth, and doesn't have the chance of dropping the cap or something. Remember that real urine can be stored in the fridge for about a week, and the freezer for up to a year, so you do not have to time it so close with your donor. Also be sure to test with validity strips (I use UrineCheck 7) if possible, no sense in subbing with a diluted sample.