Laugh like a drain
Definition 1 of 1
Pro Tip 1/3Vivid Imagery
The phrase paints a picture of uncontrollable laughter, almost like water gushing out. 
He laughed like a drain, unable to stop the giggles.
Pro Tip 2/3British Origin
It's a British idiomatic expression not commonly used or understood by non-British speakers. 
My British friend laughed like a drain at the comedy show.
Pro Tip 3/3Casual Setting
The phrase is informal and best used in casual conversation or informal writing. 
At the party, we all laughed like a drain at the silly games.