Hey, this is my Singed tanking guide. I have never posted on Mobafire before, mostly because most of my builds come from here. A couple months ago, i picked up Singed, and I fell in love. Since then, my win/loss with singed is about 10/3. Yes, it is indeed possible for a tank to carry... just not necessarily with kills.

Pros:

Snowballs well with a level 3-5 kill.
He can tank turrets for a very long time after frozen heart.
Poison Trail and diving makes you seem more like a threat than you are, causing a large degree of focus (which you can handle).
Fling will earn your team a kill almost every time it is used correctly, and can even keep enemies inside AOEs such as a nunu ult.
Enough move speed to catch any champ.
DON'T CHASE SINGED.

cons:

Not that scary early game, unless he has first blood.
Countered in lane by anything ranged.
TO win in lane, you have to take some risks.
If your team doesn't have good damage output, there isn't much you can do (like in my last game, where i went 12/5/8 and still lost).
Causes a degree of overconfidence that must be kept in check, at least for me.