Do you mean a hopper with the pipe going into it? I still have one on my
upstairs sink. Two possible reasons, Somewhere for noxious fumes to come
out, and a simple way to allow for blockages as you suggest.
My drainpipe has a cranked piece of pipe going up above the gutter to take
the fumes away, but it only takes stuff from the toilet and one would not
want an open hopper on that near a window, but for drains from baths and
sinks its ok usually.
Incidentally, I live in a terrace of four houses, but only the end two have
drains from the gutter, resulting in, when it rains heavily it cascading
down on right angled bends near my inset porch. I put in an extra drain pipe
here into a soak away, however the shrub loved the water so much, a
camellia, its now taken over the soak away and we get a nice little flood by
the front wall.
Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

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"Commander Kinsey" wrote in message
newsp.0jb2xvjcwdg98l@glass...
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