Soap is hash that has been mixed with all sorts of junk (including bee's wax, boot polish, coffee, milk powder, asprine, paraffin wax, etc). Soap purification removes the impurities from hash, leaving behind a more pure product. This FAQ will describe how to purify your hash.
You will need:
Boil the kettle and fill a large bowl with the boiled water and then add the soap. Allow the soap to soak and soften for 2 minutes or so, then crush it as well as you can with the fork into a powdery form. Stir the mix for between 5 - 10 minutes (longer if you want).
The water should turn color - that's all the crap that your hash was cut with!
The hash should be clumped in the bottom of the bowl, most of the impurities should be dissolved into the warm water. Pour as much of the liquid down the sink as you can without losing the mass hash, and then pour the rest through the coffee filter.
Shape the hash and use a towel to remove much of the water. Leave to dry (or use a blow drier for a quicker dry).
The cleaned hash may be powdery or flakey (and not remain as a compressed lump). A good method to solidify the hash is to put all the hash in to some tinfoil (nice and tight), heat the tinfoil gently and then squeeze to hash down (using a book), then leave to cool.
The hash should be more pure; you will notice that the remaining amount is smaller that what you started with. Less quantity, better quality.
Note: if the hash has been cut really bad, you may want to repeat.
How it works:
THC will not dissolve into water; dissolving the soap into hot water separates most of the impurities from the hash.