If you finished a bottle of liquid laundry detergent don't throw it away!
Instead fill it up with some water (depending on how much detergent is still left in there, there is always a little rest stuck to the bottle).
I use this newly won solution for cleaning all kinds of things, it especially works well on our steel kitchen counters! Never do I get them so clean and shiny with anything else, its amazing.
It seems that the enzymes in the detergent break down the dirt into smaller, more water-soluble pieces which can then be washed away more easy.
Plus, it smells sooo good! :)