@tsarstepan,
True! I was once making repairs to the overflow outlet of a rainwater tank (set into the ground - 120,000 gallons) and stuck my hand up the pipe to drag out whatever was blocking it... out with my handful of leaves etc came a snake!
Apparently they go into such places looking for frogs!
You have been the victim of one of those 'clowns' that go around blowing up letterboxes