tailhole

noun2

1. •
   (informal, slang) The anus of an animal, below its tail.

   • The whole hog, lips, tits, and tailhole. — 1962
2. •
   An opening in a garment for a tail to go through.

   • The colliefem drew the curtain and looked out at the moon hanging over the Pacific. […] She tossed the bra to the poolside and reached down to undo the Velcro on her panties' tailhole. — 2004