0Yorkshire Lass 4 years ago I use caustic soda (NaOH), otherwise known as sodium hydroxide or in the USA (I believe) lye. It's in the form of white granules and in the UK you can buy it in a small tub from hardware stores and the likes of Wilkinsons. But it's evil stuff if not handled correctly, it will attack skin as well as hair. Wear safety glasses and protective gloves and don't let the solution splash. Half fill a glass measuring jug with water and tip 100g or so of caustic in slowly, stirring with a metal spoon until it has dissolved. NEVER add water to caustic granules, always the other way around. The solution will get quite hot. If it seems so hot that it's going to distort plastic drainage pipes, dilute it with some cold water. Then pour it down the drain and leave it until the blockage goes, or overnight, before rinsing with lots of water.