Overflowing drain gully

[Makeitgo]

Here are some photos. I've tried putting an endoscopic camera down to look for any issues but the bend where it drops down underground presents a challenge I can't get past.

It is worth stressing that a lot of water comes down there from the flat roof and two sides of the main roof. I wonder if it is some strange pressure issue? As I say, works fine as soon as I remove the insert and continues to work fine once I put it back in - with continued flow from downpipe.

Just looking at Screenshot_20230817-170213_Gallery.jpg the side view if the set-up, it could be the camera angle but it doesn’t look like there’s much fall on the first section of 110mm from the gully to the 15° bend. I also notice that there’s a short section of 110mm at right angles to the main pipe being used to prop up the assembly before the rubber connector. Is this how you found it after the installation?

Just wondering if you’ve tried sitting a spirit level on this section? As an aside, It always amazes me how little fall is required to do the job with foul waste pipes, but I’ve found with rainwater the more the merrier within reason, as the flow can be very peaky, so what about having as much fall as you can get away with? As a flexible rubber coupler i s present, is it worth approaching the installer to see if the 110mm pipe prop could be replaced with something smaller (lower) to increase the fall? In fact, could you get the installer back in to ask why this issue is occurring?

What’s bothers me is that I’d go for what Ivor said, i.e. lift the cover of the inspection chamber (wherever that is) to see what’s happening there, however, your observations upstream kind of point to the insert itself being an issue. I do wonder if hypothetically, you swapped in a gully of another design, this issue would just go away?

 

[berty3000]

Thanks for the feedback, pal.

I agree, that photo gives the impression there's no fall, but I think it's misleading. Besides, there's still the question of why all is fine with normal rain, and fine in heavy rain if the insert is removed and then put back again?

Incidentally, that pipe running underneath goes from the front garden, down the side of the house, and to the back garden. The front was a waterlogged lawn and the idea was to shift water from front to the lower and drier back garden. The front has had the lawn replaced by land drains, rubble/muck stuff, membrane sheet, and gravel. That pipe you see has to run beneath two drains, which each serve the roof. One of those drains we are discussing. An inspection chamber is at the front garden.

The previous gully was a clay p-trap. It, and the other gully near the front garden, were replaced as part of the works. This shouldn't have been done as there didn't seem to be anything wrong with them. They were encased in concrete and each went to their own outlet at the boundary with next door. The company smashed them up, replaced with plastic, and combined with the drainage of the front garden, fed it all into one of the clay outlets. This didn't work in heavy rain, with the inspection chamber and one of the gullies overflowing. It also involved an illegal connection into the combined sewer since it involved sending the garden drainage into it without consent.

I contacted the company drawing his attention to the problems and regulatory matter. He came out and we agreed that he would reinstate the two clay drains in plastic to the two separate outlets, and keep the garden drainage separate, sending it out to a soakaway in the back. This remediation was completed, which seemed fine, but I later discovered:

a) the front gully is only one brick below DPC - the original one wasn't. Could be a headache in future.

b) this gully we are discussing is overflowing during heavy rain, unclear why as it now goes straight to the outlet.

There are some other things I could mention about the conduct of this company and its staff - a VAT registered company with an apparently decent reputation - but I don't want to drag this post on. Staff were totally unprofessional and caused some damage to driveway and front wall.

I've contacted the owner by phone, text and now email requesting a response to address these outstanding issues. I paid them a load of money. He doesn't respond to any of it.

Ideas about how I get redress on this? I'll be leaving negative feedback online, but probably need to get a third party involved and then recover costs in the small claims court presumably? I will probably send one last email first giving four weeks to resolve the issues.

 

[Ivor Windybottom]

I think the pipe's airlocked. So when it's trickling the air can move about OK to allow the flow. But when it's running heavily, the air can't do whatever it needs to do so it backs up. Removing the insert creates a path for the air to be able to get in or out of the pipe via the gully, letting the water in.

In other words it's nothing to do with a blockage or flow rate, it's that there's nowhere for the air to go to allow the flow of the water.

Where's the nearest stink pipe? i.e. a tall pipe that runs up to the roofline with a completely open vent? You may need to make a new one somewhere near. An air admittance valve doesn't really count, that is only for the benefit of the indoor plumbing, not the underground pipe. It may be that it actually needs to draw air in behind the flow, or out ahead of it, an open vent will allow it to do whatever it needs, an AAV only allows air in which may not be what's needed.

You could test this theory by temporarily inserting a tee somewhere along that pipe, with an open end pointing upwards, perhaps with a vent or cowl to keep the rats in or out (seriously!). It will smell, but I'm betting it will all just work, proving that ventilation is needed. Then you add a proper one somewhere.

 

[berty3000]

Stink pipe is on other side of the house.

 

[Ivor Windybottom]

Put a vent in temporarily, I reckon the problem will go away. If so then it needs venting properly somehow.

I reckon the problem is that pretty unusual vertical drop, the air in your pipe will never blow downwards once there's a load of water around, so it stays in that raised pipe. Perhaps a 45 degree would work better, but I can see you have obstacles to work around.

 

[Makeitgo]

Crikey Berty, lots to unpack there, looks like the gully is just the tip of the iceberg probs wise. My condolences, I feel for you ending up in this predicament. I live in a Victorian house with 4 flats/freeholds (collective enfranchisement) so we’re all responsible for costs for all the communal areas. We had a rain water runoff gully pipe that failed due to tree roots which was a nightmare. I found myself best placed to get it sorted (with myself hands on, plus a couple of contractors) and I know none of this work is cheap. Best of luck with the small claims court when the time’s right. Hope there’s someone on here that might be helpful with this aspect.

I think Ivor might have a point. Before he posted I was thinking that maybe you could try removing the rubber coupler as a test, so the downstream path was taken out of the equation. I wonder whether it would still exhibit the same behaviour? This would be a less specific way of testing than Ivor has wisely suggested (definitely worth a try) but perhaps quicker to trial. Looks like you’ve removed most of the surrounding soil and bedding shingle, so would it be that much hassle to separate the pipe from the coupler to test?

Ivor – Not sure where you envisage putting a vent? Do you mean in the top of the near horizontal section after the gully and before the 15° bend? Do you also mean something like cutting a 38mm hole in it so that after the test, you could install a 110mm drill-in strap boss, then after the test, cap the boss off maybe?

 

[Hugh Jaleak]

No reason why it should handle the flow, you've got a rainwater downpipe discharging into a outlet that's essentially twice it's size. Is the bottom of the gully clear? One possibility is, the insert is sitting in some debris, so the water cannot get under and back up to the outlet fast enough. Also could be worth checking the clearance at the bottom of the insert, make sure there is enough room there, and it's not a faulty/wrong inset that's preventing adequate flow through the gully.

Otherwise I cannot see any reason why it wont work as intended, problem doesn't appear to be with the outgoing pipework as it works fine when inset is removed from the pot, if there was an issue the problem would manifest all the time.

 

[Makeitgo]

Hugh, re the possibility of the wrong insert, yes installers sound a right shower, so could well be. I'm assuming Berty has already checked for debris etc. Guess the only way to diagnose this is to isolate each section trial and error style. Would have to be way unlucky to have got a faulty one, although it can happen obviously.

When I was testing our 68mm downpipe and gully, I found a couple of empty 10L AdBlue canisters or water poured into the gutter above served as a good simulation of a deluge. If you ask permission to raid the bins at Halfords just before their refuse collection day (I found staff very accommodating to disclose this) you can usually find a couple, but try and get the ones that still have the spouts attached as they are handy to pour with. NB - AdBlue is fairly innocuous as it's just urea and water, so a quick swish to rinse and you're sorted for a pee free smelling bottle.

 

[berty3000]

Gentlemen,

Thank you so much for taking the time to offer your thoughts and ideas - very much appreciated.

Like Hugh, I have questioned whether the insert is the right one. The company that did it probably have loads of gullies and inserts lying around at their base and maybe I've ended up with a slightly wrong combo. I did also find a couple of little pebbles at the bottom of the trap, along with a mm or so of silty grit stuff. Doesn't seem anywhere near enough to have mattered.

I'll see what happens now next time there's a deluge, which won't be long round my way! If it still overflows, I will begin by finding myself a new insert which is definitely the correct type. Failing that, I have the air lock test recommended to try out - two suggested ways of achieving this.

Another thing I will try is to see if I can get my endoscopic camera down there after all. Could be some piece of membrane sheet or such left in there contributing to air pressure issue during heavy flow.

Thanks again

 

[berty3000]

Makeitgo - think we posted at the same time. Thanks for further feedback.

 

[Makeitgo]

Hey Berty, best of luck with it, let us know how you get on.

 

[Ivor Windybottom]

Can you see or feel how big the gap is between the bottom of the insert and the gully base? Obviously if there's a very small gap it isn't going to work properly.

But I'm still thinking a downstream partial blockage or air pressure could be issues.

 

[Hugh Jaleak]

Check the gap between insert and base of pot, if you think it is too small, remove insert a cut a slice off the bottom, then re insert and see if that helps.