Overflowing drain gully

[berty3000]

Hello,

I have recently had a plastic bottle gully and drain installed connecting to the combined sewer. The downpipe serves a flat roofed extension and part of the main roof so gets a lot of water during downpours. I've noticed in heavy rain that the gully is overflowing a bit, but if I reach in and pull out the grey plastic insert, then put it back in, the problem immediately goes away. Like it is being caused by an airlock or something. There's nothing in there like debris, just the inner grey sleeve thing which has fins down the side and goes in track things within the main gully.

How do I prevent this so I don't have to go fiddling about in the rain?

Thanks

 

[Dereekoo]

Leave out the insert and see if you get any odour problems

 

[noseall]

Hello,

I have recently had a plastic bottle gully and drain installed connecting to the combined sewer. The downpipe serves a flat roofed extension and part of the main roof so gets a lot of water during downpours. I've noticed in heavy rain that the gully is overflowing a bit, but if I reach in and pull out the grey plastic insert, then put it back in, the problem immediately goes away. Like it is being caused by an airlock or something. There's nothing in there like debris, just the inner grey sleeve thing which has fins down the side and goes in track things within the main gully.

How do I prevent this so I don't have to go fiddling about in the rain?

Thanks

The gully and trap are doing their job i.e. collecting the debris and telling you when to remove it.

 

[Makeitgo]

Did you see the installer of the new bottle gully and drain perform a flow test (sloshing a high peak volume of water down it) after their installation? Did you have any issues with the water running away to the sewer before the new install? Just wondering if there is an incorrect fall from the gully exit to the sewer maybe…

 

[berty3000]

Did you see the installer of the new bottle gully and drain perform a flow test (sloshing a high peak volume of water down it) after their installation? Did you have any issues with the water running away to the sewer before the new install? Just wondering if there is an incorrect fall from the gully exit to the sewer maybe…

Not that I know of to both questions, but not certain. I doubt there's any problem with the fall based on what I saw. Flows downwards to outlet.

If I remove the insert as the overflowing occurs and then immediately put it back as it was, the overflowing stops with the same volume of water going down. It seems to be something to do with the insert combined with the volume of water during heavy downpour. But as mentioned, if pulled up then pushed back in, problem solved.

I'm tempted by Derekoo's idea of just leaving the insert out.

 

[Makeitgo]

Hmm, sounds odd as you would have thought the insert design would be free of bad turbulence impeding the flow. You could try it without the insert, but I would make a close fitting, simple chicken wire mesh to fit in there to prevent leaves and other debris entering during the test period. Oh, and teather the mesh to the down pipe with wire or somthing because you really don't want that accidentally falling down there either : - )

 

[berty3000]

Hmm, sounds odd as you would have thought the insert design would be free of bad turbulence impeding the flow. You could try it without the insert, but I would make a close fitting, simple chicken wire mesh to fit in there to prevent leaves and other debris entering during the test period. Oh, and teather the mesh to the down pipe with wire or somthing because you really don't want that accidentally falling down there either : - )

Nice idea. I could just make a cylindrical chicken wire inside that is up against the inside of the gully don't think that could anywhere.

 

[Makeitgo]

Nice idea. I could just make a cylindrical chicken wire inside that is up against the inside of the gully don't think that could anywhere.

Best of luck

 

[noseall]

Chicken wire wont collect harmful (damaging) silt?

 

[berty3000]

Won't silt still sit at the bottom of the bottle gully? Also, is it harmful to the combined sewer which the gully is connected to?

 

[Hugh Jaleak]

Pic may help, but does the rainwater downpipe discharge above or below the grid? Gully should handle the flow from a 68mm downpipe without issue, so wondering if there is another issue.

 

[Dereekoo]

Pic may help, but does the rainwater downpipe discharge above or below the grid? Gully should handle the flow from a 68mm downpipe without issue, so wondering if there is another issue.

Yes, it doesn't

 

[Ivor Windybottom]

The purpose of a trap is not primarily to keep hold of bits or silt, the main reason for its existence is to prevent the stinking air from the combined sewer from venting out of it, as it will without the insert. You'll end up with a smelly garden (and house if the window's open).

I'd suggest you need to check what's downstream from it, hopefully there's an inspection chamber further down? Get the lid off the next time it's raining heavily, see what's going on. There may be a partial blockage a lot further down, perhaps lifting the insert just lets the contents of the drain into what would normally be airspace if it's fitted, or it's some other strange pressure related thing.

 

[berty3000]

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.

 

[Makeitgo]

Won't silt still sit at the bottom of the bottle gully? Also, is it harmful to the combined sewer which the gully is connected to?

Quite right, so the substituting of the insert for the chicken wire (or finer mesh maybe) should be for a short test period only - silt build up is accumulative. If you know there’s a chance of an unusually excessive amount of silt that’s going to be present while testing, then testing this way could be an issue.