turn on the waterworks
Start to weep, as in Whenever Dad refuses a request of hers she turns on the waterworks. This term implies that one begins to weep deliberately, as though switching on a system of pipes connected to reservoirs.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.