I've used my (fairly new) Yankee tank probably three times over the past three years, and haven't had any problems yet with uneven development. I was using Tmax 100 4x5, and the developer was Dektol. I even filled the tank through the small hole in the top with the lights on. I was simply following instructions, and possibly lucked out. I've got some of the new EDU 200 negs to try with Xtol, so we'll see what happens!