I have all penguins -- the mini in my 5g and 220s in my 36g -- when I first started a few months ago, I had the wheel in my mini stop while I was at work -- no idea for how long. I had a goldfish my daughter won at a carnival and was just learning my lessons (and yes, I lost the goldfish). Couldn't learn things fast enough to save her. Now that I've started learning things BEFORE doing them, things are MUCH better! I don't have any problem with my wheels now -- every water change, I swish the carbon filter in the siphoned water or change it out. Amazing how things work when you "use as directed"!
I should have specified the question to elkhound, but that's fine. the penguins use the outflow to spin the wheels as you pointed out. The emporers actually have spray bars that direct water onto the wheels from the impeller cavity. With the emps you could feasably stop all flow through the mechanical cartidges and still have water happily spinning you bio-wheels. I tend to think emporer rather than penguin when someone asks a bio-wheel question.
Dave