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Discuss Underground drainage advice please. in the Plumbing Forum area at PlumbersForums.net

mutley racers

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Hi all. I have not done any drainage as of yet but will be next week.

I am taking out a macerator and instead installing a soil stack and underground drainage to an existing man hole.

Q1) can I use a short radius (rest) bend at the foot of a stack? When looking online it does say that this is what they are for. But there are also long radius bends which you can use.

Q2) How far below ground does the drainage pipe have to be?

Q3) Can I use sand to lay the pipe on and then cover it with sand or should it be pea shingle? Maybe pea shingle will go a lot further.

Q4) I am hoping to pop through the side of the manhole close to 2/3s the way up and drop down and chase shoe into the benching. Does anyone know what mix this benching is? I know there is a name for this installation but I cannot think of it.

Cheers all
 
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mutley racers

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I was thinking of putting in an internal backdrop connection but from reading online it is frowned upon. Don't fancy digging down down down though
 

SimonG

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Last one they just had me core through side of manhole, push pipe through and terminate with a 90° bend pointing down.
 
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mutley racers

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Last one they just had me core through side of manhole, push pipe through and terminate with a 90° bend pointing down.
Oh really, now that would be nice but doubt that will be the case here. Will call them up today
 

Ben-gee

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Are you looking to get it done to pass building control or are you looking for trouble free future? (ie is it your own place).
If the former, do whatever they let you get away with.
If the latter, dig down and do it properly. The “least work” robust way is to dig right down at manhole so as to enter horizontally at sewer pipe level. A couple of feet away from this you can then employ the ‘back drop’ method with no worries - better if you use a nice slow bend at the base of back drop and you also need to add rodding access to this (basically at top of back drop use a branch rather than bend, with rod point on vertical section).
I did this at home 7 years ago and no problem since (why did I write that down...)
 
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mutley racers

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GSR
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Are you looking to get it done to pass building control or are you looking for trouble free future? (ie is it your own place).
If the former, do whatever they let you get away with.
If the latter, dig down and do it properly. The “least work” robust way is to dig right down at manhole so as to enter horizontally at sewer pipe level. A couple of feet away from this you can then employ the ‘back drop’ method with no worries - better if you use a nice slow bend at the base of back drop and you also need to add rodding access to this (basically at top of back drop use a branch rather than bend, with rod point on vertical section).
I did this at home 7 years ago and no problem since (why did I write that down...)

Hi, thanks for the reply. It is at a client's so belt and braces and with regs
 
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mutley racers

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Called them and they say I can do internal backdrop as long as there is still room for access. Not sure what space it is you need but it is a standard manhole drain so I would have thought big enuf
 

Ben-gee

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Don’t forget they are satisfied if there is access to jet it, expensive, better if there is access to rod it.
 

NickH

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How much space you need depends on the depth of the manhole. Over a certain depth you have to have enough space for a "man" to get down the hole so in theory an internal backdrop might encroach on that.
How deep is the manhole ?
A normal rest bend isn't a short radius bend, two different things. Use a rest bend as they are easier to rod.
 
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mutley racers

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Thanks for the advice so far guys.

So reading up on drainage, it is most likely I can do an internal backdrop as the man hole is about 600 x 900 and about 1.6 metres deep.

Upon reading, it says I need a flexible connection 150mm away from where the pipe enters the manhole. Does anyone know where I can find one of these?

Also, what are the fittings called that you cut into the benching? Or can I just cut a spigot elbow in half to create this open channel?

Cheers
 
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mutley racers

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Another question guys. I will be running a new toilet soil pipe out of a pitched roof to the stack. Do I use a pitched roof slate but reverse it so the pitch is pointing down and then I shall get the slope to the toilet? Or do I use a flat roof one
 

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