caustic soda , less than £2 from the chemist del but its proper nasty stuff so be carefull
and i mean be carefull in the sense that itl melt your skin
i did a load of stuff a few weeks ago in the sink , filled with water then add some powder and placed the bits in , took a while to get going but in half hour it would strip . then id pull them out ( i tied them all to bits of string but watered down it isnt as hazardous ) then i run them under the tap in the bath ( i was also doing a rim ) to stop the soda corroding away the alloy and to wash off the black that gets left behind
lock away the anodised bits you dont want to strip as you might get into it like i did and wander around the house looking for parts that would look better polished
pull the plug and the drain gets a clean as caustic soda is just the active ingredient of drain cleaner