Make sure you have a container that will take the whole seat and preferably one that can be used on the stove
Put one of them tall containers of salt in the pan along with the dye, then add boiling water and stir, add your seat (fully submerged) and simmer on the stove for about 30/60 mins then take it out (as long as its gone jet black) and plunge it straight into cold water then leave to dry