I had a weird black yeast ring in my Brew Bucket the first use as well. Hasn't happened since, which makes me think the SS just wasn't sufficiently passivated,even thought used BKF and StarSan. Didn't hurt the beer though.
And the EvaDry is a waste of money -- does nothing in my keezer. Spend $10 on some silica gel kitty litter (same stuff) at Petsmart/ Petco, toss it into an old tube sock, and you've got 10x the dehumidifying power. Works great.
That's a great idea!