On Saturday, 23 May 2020 15:12:51 UTC+1, Clive Arthur wrote:
I have some drain unblocking poles, but any camera would need a remotely
operated lens cover to stop it getting filthy on the way up.
Any such thing around? USB would be good, maybe it's a little too far.

Invert a plastic bag over the camera. Attach a length of hose to the drain rods with the end inside the plastic bag (you might run the cable inside the hose to give it protection).

When the camera has exited the chimbley pot, send some compressed air up the hose to blow the bag off. You'd probably have enough force to blow off a bubble-wrap bag.

This is a once-only operation.

Or attach something shiny and wait for a magpie or jackdaw.

Or attach a (potato) chip and wait for a gull.

Owain