You have to pick:

When you turn in a penguin. Do you fall into the toilet seat or are you the same size as you were as a human. Also what are you when you wipe? Because i doubt a penguin could use paper and reach their own bung holes with their none existing bird hands. Though they'd have pointy no cheek butts so there'd probably not be much to wipe up. Maybe you just press your penguin butt on to the paper you laid out on the floor.
Are you still a sentient being or do you have the mind of a penguin? Will there be feces on the walls when you turn humans again? Do penguins eat poo?

I guess if you were a penguin when you pooped. No one would ever catch your human self crapping. So you could actually admit that you don't crap. Because your not you when you do.

I think the worst is that you turn into a penguin when you HAVE to poop, not just while pooping. That could happen unexpectedly.