rectal dilator rectal dilator a rectal or anal dilator is a medical device similar to a speculum designed to open and relax the internal/external anal sphincter and rectum in order to facilitate medical inspection or relieve constipation. one early version of a rectal dilator was dr. young's ideal rectal dilators, invented in 1892. a set of antique rectal dilators exhibited at glore psychiatric museum. rectal dilators are also used as sex toys.