Although composite sink material is completely scratch resistant it
can be a bitch to clean. Surface stains can be removed by soaking with
biological washing powder in boiling water, but over a period a hard
layer of staining can appear on the drainer. I’ve found these
impossible to remove with any chemicals, even caustic soda, although
they can be removed by scraping with a chisel without causing any
scratching. This is quite laborious so there may be some power tool
which would save the elbow grease.