Why did drainpipes used to have a box on the wall?

It might have been to avoid sewer gases from flowing up the drain pipes from sinks if the water in the U trap got blown/sucked out. I'm not sure why it was fairly common (or even universal) for older plumbing but is very rare on modern plumbing, even on houses with external drain pipes.

I will make a confession. When I was very little (maybe around 5 years old) I used to have an infatuation with plumbing, and knew various houses on my walk between home and school not by who lived there but by the pattern that the pipes made on the wall. Embarrassing to admit such nerdy behaviour! There were some houses that had steeply-sloping pipes from sink/bath directly into the vertical soil pipe, but which had a second pipe that branched off the sloping pipe and entered the soil pipe higher up. That always intrigued me. I wonder if it was a way of avoiding the U-trap water from being sucked out.

It was even done for rainwater pipes:

I fail to see why this helps. Let's say I try to empty my bath, but the downpipe is blocked outside. I'd rather the bath just didn't empty, then I'd investigate the problem. I don't want the water to come sloshing out all over whatever is below it outside, which could even be people.

It could make sense to stop water going back the wrong way - eg. a 3rd floor bath emptying into a 2nd floor bath and flooding the room. But there's no point on the highest floor, which is where I've always seen it.

Perhaps the venting wasn't so good in those days? Although I don't see why, the vent pipe sticking up to roof height has always been pretty much the same.

Sounds sensible to me. When the mind is doing nothing during your walk, it's going to think about something.

That makes sense, a smaller version of the big pipe that's usually placed just after a toilet. When the sink finished emptying, the water flowing through that steep pipe and filling it's whole diameter, would suck the air behind it. But the extra pipe allowed air in from higher up instead of pulling on the u-bend water.

I don't see the point in that. If the downpipe became blocked, all that does is make loads of water pour out of the box instead of just spilling from the gutters over a wider area. I'd say it makes the problem worse.

What's the advantage of your waste spilling all over the garden instead of just not leaving the bath?

So why on the top floor? As in the photo below and the house I remember seeing it on.

If the pipe is blocked and you empty your bath, then if you have a box, the water goes everywhere outside. If you have no box, the bath just stays full and you call a plumber. The second one is preferable obviously.

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

Good point, I hadn't thought of roof water going into the sinks and baths.

It's a British thing, obviously.

Here the rainwater pipes do NOT connect to sanitary sewers AT ALL

My gutter pours onto the postman waiting at the door.

Until your wife gets your dirty bathwater all over her when she's gardening.

I don't want a bath full of water all over my garden.

What is? It's not clear what you're referring to. And stop deleting the newsgroups. uk.d-i-y re-added, which is where Jim is from you Canadian f****it.

Nothing to do with a box, there's a leak in the gutter. And a box would mean it would pour out all in one place.

You don't need a plumber to unclog a drain. And you don't need a bath every day, you can wait 1 day extra and get him out on Monday.

WHY do you CAPITALISE for NO reason?

And nowadays we do have seperate piping. Costs more to install two sets of pipes under the road, but saves money having to clean less waste, but when someone connects something to the wrong pipe as I've done for convenience, sewage goes into the sea.

P.S. you just replied to someone in a uk group and removed that group, so he didn't see your reply. F****it.

Just how long does it take you to get a plumber? I can get one within 24 hours unless it's a Sunday. Short enough time to go without a bath.

Or you could just fix it yourself. How helpless do you have to be to not be able to unblock a drain?

It's where the drain happens to be, you don't get a choice.