On Tue, 21 Apr 2020 09:52:53 +0100, Xeno wrote:

On 21/4/20 4:27 am, ARW wrote:
On 19/04/2020 20:46, charles wrote:
In article op.0jb2xvjcwdg98l@glass,
Commander Kinsey wrote:
Why did drainpipes used to have a box on the wall, some sort of
overflow if blocked? See link below for an example photo.
https://www.dropbox.com/s/1jry8zas14bmivc/box.jpg?dl=0

I still have them. It provides an air break to prevent feedback.


There is some suggestion on certain web sites that it is to increase
flow rate.

The air break will assist in that.

How?