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Far and away the most common type of waste, a slotted waste is suitable for use with a basin that has an overflow. The slot in the waste allows any excess water from the overflow to drain into the waste pipe when the plug is closed.
Slotted wastes can come in a variety of designs, including turn over and pop up models which you press to plug.
link:http://www.basindrain.com
bathroom plumbing accessories basin slotted waste