What Size Drain Snake Should You Use? Plumbing Q & A ©Depositphotos.com/davisales Your Question– “Does a drain snake have to fill most of the pipe to be fully effective – or can one use a 1.5cm diameter drain snake to clear a pipe that is 6cm diameter?” Our Answer– In our opinion, you need a bigger drain snake. Ask the Plumber2018-03-05T18:13:33+00:00