Couple of things I don't understand about my drains

[Michael D]

Today I finally rodded my drains (not done for at least 5 1/2 years and maybe decades). There are a couple of things confusing me:

1. In the inspection chamber before going into the street I found 2 pipes, one above the other. Pls see the photo here: lower hole has got white foam in). Is the upper hole some kind of overflow?

1. When I lifted the cover off I couldn't see the lower hole. It was obscured by gunk and what I thought was a shard of broken pipe. When I cleaned things out I found the shard of pipe was actually the cap / cover thing in the 2nd photo. It was on its edge at an angle of about

45 degs to the opening of the pipe. I've no idea what it is or whether it's supposed to be there.

Any ideas?

Michael

[Andy Cap]

The top hole is for rodding, by-passing the trap at the bottom.

The round bit is a lid that should normally be in the top hole, but which had fallen out, partially blocking the drain.

Put it back and all should be well.

Andy C

[dom]

It's an interceptor trap:

[Roger Mills]

Like he said. I think you've got what's called an external backdrop - where the input pipe is higher than invert level, and drops down just outside the chamber - with a rodding point in line with the pipe. This is illustrated - albeit with a bigger drop - here: (see Fig 16)

[The Natural Philosopher]

Nice one. Hadn't seen that style before.

Modern practcie is to have sealed drains and appliance traps.

[Matty F]

JPGs on an HTML web page?

[Jim K]

works for me - are you putting enough coal on? ;>)

Jim K

[Andy Burns]

[Michael D]

Ahhhhh - that explains it. Many thanks for the swift responses.

One other question: how should I re-attach the cap? If I just push it back in it probably won't be a very good fit & may fall out again. Should it be fully or partially mortared in to prevent smells getting back through? I don't know if something more modern like mastic may work as it would make it easy to get out.

Michael

[dom]

I wouldn't bother with the cap. AIUI, the modern solution would be straight-through with no trap at all (unless there was a special requirement like grease-traps for restaurants). I would do my best to clear out the trap and get everything flowing as freely as possible though.

[Phil L]

It's purpose is to prevent rats and debris getting into the drains. If you look at the pictures of interceptors, you'll see that there is a water trap to prevent sewer gases getting through. Don't mortar it in or use any other kind of adhesive or you may never get it off again, if you like you can lean a housebrick against it

[The Natural Philosopher]

yes. The only downside is pongs. If these are floating up from gulleys or plugholes, then consider trapping those individually. Or source a rubber plug from somewhere that fits. Or modify what you have to take a standard rodding point.

[The Natural Philosopher]

which is bypassed by that pipe.. so its just as much to stop the pongs getting through as well. The cap, that is.

I wonder if at some point the thing flooded, and someone poked around, the cap fell off, and it drained and they left it like that.

Frankly the whole concept is defunct these days anyway, so its moot as to whether what is upstream is well enough trapped so the whole shebang is a redundant but of potential blockage.

[Phil L]

Forgot about those. To the OP, you can buy a rubber bung with a butterfly screw which tightens and seals the hole, they are made specifically for drains and you can get one from any builders merchant, or maybe even b&q.

Look for drain test plug on google, a 200mm (4 in) one will set you back about 8 - 10 quid

[Phil L]

typo fixed, 100mm not 200mm

[The Natural Philosopher]

And I forgot about those!

15-all ? :-)

[Phil L]

Ye ok :-p

[dom]

Is this a good idea?

The trap will be prone to blocking from time to time (because it's inline, with no great pressure acting on it).

When it does block, the chamber will start to fill.

When the chamber is deep (in s***), you want to *easily* remove that plug and allow the chamber to drain.

Perhaps you could arrange a pull-cord to retrieve it, if the fit isn't too tight.