manholes

[G&M]

I want to connect a new drain using the standard brown underground 100mm PVC pipe to an existing manhold leading to my septic tank. This manhole has two pipes joining with a cutaway PVC right angle join near the upstream end of the manhole and I would like to join in downstream of this where there is room in the manhole.

The H building regs cover most things in detail on laying the pipe underground, passing through walls and suchlike right up to the manhole, (and indeed everything at the septic tank end as well) but don't really cover the prefered construction of modification of the manhole itself.

Is there a document somewhere that shows best practice for doing this ?

[The Natural Philosopher]

Not really. All a manhole has to do is allow access to pipes where changes in direction occur.

Most people merely bed down pre-made plastic units in gravel and or concrete, and that's that.

[Rick Dipper]

I modifed an old, and built 3 new man holes last year, all were inspected, all were fine, I had never done it before, and just did what seemed sensible. I do not claim to be a builder.

The cutaway is there for cleaning, and watching the stuff go by if your under 7 and find these things amazing. I ran my cut aways right to the edge of the manhole. I made my cutaways using 110mm pipes that I cut down, and mitred the joins. I then cemented them in. To cement them I got the cement in and when drying used a sponge to smooth all the cement. Any gaps/joins were done with cement. One thing, don't have even a drop of water come down the pipes before its very dry.

IN one man hole I have the entry pipe up high, and it just stops. The "stuff" drops down into a funnel shape for the exit pipe which is right at the bottom. However at this point I have clean water with no solids so they were much more relaxed about what I did.

Rick

[G&M]

I was assuming there was some minimum height the new pipe had to be above the existing one, or perhaps a minimum angle, or anything else, to prevent backflow and so on. Problem is top of the pipe of the existing system is only 4 inches from the garage floor surface anyway so there isn't much leeway to create much of a drop and so was after the minimum needed.

[G&M]

document somewhere that shows best practice for doing this ?

That sounds exactly like I would like to do as I don't have the height for a drop. I was proposing to cutaway a 90 deg join as you describe, angle grind away the existing pipe a bit and then slip the new section under the upstream and over the downstream section of the existing pipe, then connect the new system to the 90 deg joint.

Did the BCO raise any questions or comments on your system ?

[Rick Hughes]

If get an OSMA catalogue there are good guides in there ........ I would guessthat there is also good stuff on Cormais web site, he covers most aspects of drainage:

>

[G&M]

instinctively done it (apparently called a "stepped invert") was not recommended.

[G&M]

(6 grano, 2 cement, 1 building sand) but it doesn't seem very smooth compared with other manholes I've looked at and I assume the minute holes will gradually trap stuff one would rather it didn't.

Is it correct to increase the sand to get a smoother mix ? Or more cement ?