A few years ago I would casually use Caustic Soda to unblock my drains. I never gave a thought to my environment or what I put down the drains. Nowadays I know a much greener, more frugal and less harmful way to degrease my drains. This morning I needed to give the sinks a good clean as my precious child who was on wash up duty didn't clean them out properly and they were all a bit yucky. So below you see the dirty drain hole with 2 heaped tablespoons of Bicarbonate of Soda.
cleaning uses for vinegar and bicarb here.