Waste fouling benching

copea · 27 Jun 2017

Afternoon,

We've recently had a loft extension built which has added a WC on the second floor where there wasn't one before.

As a result, the waste seems to enter the manhole with a lot more gusto than before due to the extra height, and we're getting waste fouling the benching opppsite.
At the moment I'm having to wash it off every month, and when I do there's a considerable amount which has built up.

There can't be a gentle bend at the bottom of the stack as the stack enters the ground at 90 degrees to it and then changes direction within very little depth.

I've attached photos to illustrate.
Is there an easy option to prevent this happening? I can't see that there's enough depth to accommodate a regular rest bend...

Any advice welcome.

Thanks!

terryplumb · 27 Jun 2017

underground waste staining a bench ??? is there no cover on there ?

copea · 27 Jun 2017

terryplumb said:
underground waste staining a bench ???

Not sure if you're being serious or not?...

terryplumb · 27 Jun 2017

serious ,and confused , just don't understand ?

copea · 27 Jun 2017

I mean benching as in the sloping concrete sides of the manhole.
That is what it's called, isn't it?

And yes, there is a cover. I just removed it to take the photo.

terryplumb · 27 Jun 2017

ha hah , in my neck of the woods we refer to it as haunching .you are correct of course benching is also what it's called...I thought you were talking about a garden bench LOL.

copea · 27 Jun 2017

That'd be some seriously high flying turd!

Doggit · 27 Jun 2017

Is the down pipe completely stright, or can you put a slope in it to stop the high gravity drop. The only other option that I can think of, would be to alter the angle of the inlet pipe in the manhole, so that it hits the bottom of the run. Or could you bed an angled piece of slate etc in to the LH side of the manhole.

Hugh Jaleak · 27 Jun 2017

Connection to the stack in the pic doesn't comply with regs either, too low down, given depth of drains. Without rebuilding the chamber, I don't think there's any easy fix, how far is the stack from the chamber?

Nige F · 27 Jun 2017

Have a look at www.pavingexpert.com search "grano "where you will see an example of benching - what you have at the moment is quite decayed. You could cut it out and reshape with some grano mix, creating a vertical face before rounding to sloping horizontal surface. With care you can get a virtually polished surface

copea · 29 Jun 2017

Doggit said:
Is the down pipe completely stright, or can you put a slope in it to stop the high gravity drop. The only other option that I can think of, would be to alter the angle of the inlet pipe in the manhole, so that it hits the bottom of the run. Or could you bed an angled piece of slate etc in to the LH side of the manhole.

Unfortunately not. Straight down is the only option.
The slate isn't a bad idea.

Hugh Jaleak said:
Connection to the stack in the pic doesn't comply with regs either, too low down, given depth of drains. Without rebuilding the chamber, I don't think there's any easy fix, how far is the stack from the chamber?

Doesn't surprise me. I think most things were done by the previous owner with little regard for the rules.
Only consolation is that sewage is unlikely to ever back up that far as there's a bottle gully for the rainwater downpipe feeding into the same manhole, so any 'excess' would end up coming out of that.

There's only a foot or so between the stack and the closest corner of the chamber.

Nige F said:
Have a look at www.pavingexpert.com search "grano "where you will see an example of benching - what you have at the moment is quite decayed. You could cut it out and reshape with some grano mix, creating a vertical face before rounding to sloping horizontal surface. With care you can get a virtually polished surface

That could be an option, but I don't know if I'd be able to build it up high enough and still get a slope.
The invert is very close to the surface.

What I was hoping was that there would be a fix along the lines of a rainwater shoe type fitting to drop it centrally, downwards into the run.

Thanks for the help so far.

Ian H · 29 Jun 2017

The branch is very high compared to the channel but the sides look steep enough.

I did one at an office where 2 stacks were too close to the manhole. The turds jumped up onto the opposite benching and once the buildup grew it fell off and blocked the drain.

I piped them up with solid Y junctions (rather than 1/2 channel ones) and left them closed but accessible in the manhole. If there ever was a blockage I could have drilled into the junction to jet/cctv and capped it with a 54mm fernco bung once cleared.

That was 4 or 5 years ago and they haven't blocked since.

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Waste fouling benching

copea

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