Woah! Hold on people, Fish Emulsion isn't Fish Tank waste. Sometimes I wonder where you people get your ideas from!
Using water and/or waste from your aquarium to supply nutrients for growing plants is (unofficially) known as "Aquaponics" or "Guppyponics". Some people swear by it - but to be honest, i've never heard a real good explaination (one that really gets down and gives a detailed account of how it all works!). Maybe some practicioners would like to speak up!
"Fish Emulsion", like Alaska Fish Fertilizer, is a product that is made of all the "leftovers" after the edible parts of the fish have been fileted (fins, skins, heads, scales,tails and guts - all the good stuff!). All this crap is ground up and processed to become "fish emulsion", a very high Nitrogen (and stinky) fertilizer. It's really good stuff, I use it.