Heh, I was quite surprised to find how little there is on the web about this phrase! It seems to be originally UKnism (anyone demur?), and I would imagine is based on the fact that a full-throated laugh causes you to open your mouth wide in a manner reminiscent of a drain-hole! Perhaps you could pass the query to MikenMelanie or Micheal Quinion….?


“xxxxxxx
xxxxxxx
In spite of the pain,
She laughed like a drain,
When the surgeon inserted a stitch in her…..”

Anyone know the rest of this?!