Killing stumps

I've read online that bonemeal and boiling water poured into a predrilled stump will help rot the stump from the inside out, I dunno how true this is - has anyone tried it?
Failing that, I'm after a tried and tested method of chemically removing a stump - it's right on the concrete barrier of the drain* so digging it out isn't at all possible, thankfully it's only a young tree when it was still there (3yrs by the rings)

* the drain is only a a water overflow for roof water, so it's not a main drain with pipes to worry about