For tough problems, allow 30 minutes before flushing. Drano® Max Build-Up Remover works over a longer time period to prevent clogged drains.
The official website of Drano says that it can be safely used with plastic and metal pipes. You just have to read and follow the directions in the product accurately. If you follow the product’s instructions correctly, then there can be no harm in leaving Drano on your sink overnight.