In article ,
Chris Hogg wrote:
On Sun, 26 May 2019 12:23:28 +0000 (UTC),
(Richard Tobin) wrote:

Behind a panel in my house is the exposed end of a long-disused waste
pipe - quite likely there was once a sink there - which I suspect of
being the source of an occasional bad smell.

Presumably I should cap it, but as you can see from this photo it's
not a neat end:

http://www.cogsci.ed.ac.uk/~richard/pipe-end.jpg

The outside diameter is about 7cm.

There are flexible rubber caps for sale, e.g.

https://www.amazon.co.uk/Cloverleaf-...dp/B078HHNFHS/

but I doubt it could be attached securely. Would a piece of some kind
of flexible rubber sheet and a jubilee clip do the trick?

It has a jubilee clip, just like you're suggesting for a piece of
rubber sheet.

Yes, but the cap is very shallow, so the clip would be over the part
of the pipe that slopes inward - I think it might just pop off when
the clip was tightened.

In addition, you could liberally coat the flutes inside
of the cap with silicone or sticks-like-**** or gutter sealant to make
it more secure and make it air-tight. It's not as though it's going to
be subject to movement or stresses and strains, tucked away behind
that panel.

That might work.

-- Richard