On 1 Feb, 20:40, "The Medway Handyman" davidl...@no-spam-
blueyonder.co.uk wrote:
Asked to sort out a blocked downpipe on a hotel today. *Cast iron pipe
coming down from roof into a hopper, then a smaller diameter pipe down to
the ground.

If the cap had been on the bottle, it would have expanded and wedged
itself into the pipe.

Someone will shortly try your technique with a plastic drain pipe.