To laugh like a drain means to laugh in a very loud and boisterous manner, which is what she would do at the goings on of her friends.
Context: "She was a true member of the old school who would laugh uproariously and heartily at the goings on of friends." Claim: "She was truly a member of the old school who would laugh like a drain at the goings on of friends."
Considering the context, is the claim true, false, or unknown?