Drain - can I drill the grey area?

Cellophaneskies · 17 Aug 2025

Hi

Thinking of adding drainage to garden. Don’t need or want a 4 inch soil pipe for this, it will only be run off from a small patio. Looking at aco hex drains which appear to have small pipe outlets - I need to confirm this but they appear like internal water waste piping like from kitchen sink.

So basically my drain externally looks like the photo. My basic understanding is that the actual drain cooper is the brown but under the metal grate. The concrete hit around the outside isn’t the drain per se, but some surrounding ‘gulley’ added on top. So in theory I’m not tampering with drain.

I’d carefully drill a hole through and make it wider to take the pipe size of my choosing.

Does this sound sensible, any gotchas here. I don’t really want to dig this up and replace it nor do I think k need huge pipe for this, I suspect any drain off will be a trickle rather than a gush!

aveatry · 17 Aug 2025

Trying to decipher what you are saying but I have a aco drain like you are planning and it goes to a similar drain - down pipe and kitchen waste to a grid covered gully like you have but I just cut out the side of the concrete and haunched it to the linier drain.
I think the Aco drain outlet down section is 68mm like a rainwater down pipe I fashioned a debris sump from some down pipe for mine.

Cellophaneskies · 17 Aug 2025

aveatry said:
Trying to decipher what you are saying but I have a aco drain like you are planning and it goes to a similar drain - down pipe and kitchen waste to a grid covered gully like you have but I just cut out the side of the concrete and haunched it to the linier drain.
I think the Aco drain outlet down section is 68mm like a rainwater down pipe I fashioned a debris sump from some down pipe for mine.

Ok thanks. Trying to confirm if it’s silly idea to drill the grey concrete area but I can’t see that it would cause a problem unless I was really aggressive or unlucky!

aveatry · 17 Aug 2025

The aco drain is about 3 inch down from the grid top but the outlet is at the bottom of the 3 inch and the a connector so by the time you have taken that into consideration you are at about the level of your drain grid down their very difficult to drill through that given it is full of gravel stones. But instead angle grind out to the bottom of the aco 3 inch and haunch the drain around it.

noseall · 18 Aug 2025

Cellophaneskies said:
Ok thanks. Trying to confirm if it’s silly idea to drill the grey concrete area but I can’t see that it would cause a problem unless I was really aggressive or unlucky!

That three sided upstand is a pre-fab surround. It won't affect the drain gully as long as you carefully remove it. The inset mortar immediately around the gully will be added after.

Ivor Windybottom · 18 Aug 2025

If you drilled that then the most likely outcome would be that it would crack straight through from top to bottom and would forever leak dirty water from your waste pipes into the soil and/or mud and roots would enter the gully.

If you create any sort of chamber with an end open to the air then there's a good chance it will get full of leaves, mice, rats or other rubbish.

The correct way to do this would be to replace the gully with a u-bend and add a tee facing sideways above it, then a hopper above that. Then there's a trap between you and the sewer and everything is on the correct side of it, and there are no open pipes. But you can only do this if the sewage pipes are low enough to fit this arrangement between the hopper and u-bend.

The dodgy way to do it would be to couple your aco drain directly into the sewer - then your aco drain will function as a an air vent directly connected to the sewer and will stink. Sounds ridiculous but this does happen.

The simpler way would be to create a new soakaway elsewhere and run your aco drain into this. Then everything is sealed underground and separate from the sewer.

Deluks · 18 Aug 2025

In what direction does the patio currently drain to?
Do you have a persistent problem with pooling or puddles on your patio? (Alliteration hi-score!)

Digging a 4 inch pipe into the garden, drilled or slotted, wrapped with membrane and gravel would be a lot less hassle than tampering with an existing gully.

Cellophaneskies · 1 Sep 2025

Ivor Windybottom said:
If you drilled that then the most likely outcome would be that it would crack straight through from top to bottom and would forever leak dirty water from your waste pipes into the soil and/or mud and roots would enter the gully.

If you create any sort of chamber with an end open to the air then there's a good chance it will get full of leaves, mice, rats or other rubbish.

The correct way to do this would be to replace the gully with a u-bend and add a tee facing sideways above it, then a hopper above that. Then there's a trap between you and the sewer and everything is on the correct side of it, and there are no open pipes. But you can only do this if the sewage pipes are low enough to fit this arrangement between the hopper and u-bend.

The dodgy way to do it would be to couple your aco drain directly into the sewer - then your aco drain will function as a an air vent directly connected to the sewer and will stink. Sounds ridiculous but this does happen.

The simpler way would be to create a new soakaway elsewhere and run your aco drain into this. Then everything is sealed underground and separate from the sewer.

I don’t really have space for a soakaway far enough from a boundary. I’d be making the hole through the side, on one of the vertical faces.. I don’t see it as being much different to directing other water flow this way, ie if I put sink waste into it from above? Not that I’m doing that but logically it doesn’t seem much different?

Ivor Windybottom · 1 Sep 2025

The problem's the mix. Water doesn't "know" which way is the way out. It splurges all over the place.

The waste from the kitchen or bathroom pipe already there could run into your aco drain and sit in there festering.

With or without the food or human waste, the aco drain will have an end that's open to the air so could fill with whatever leaves, animals or whatever ends up in there.

Aco drains connect to an underground 110mm (4") waste pipe, not a narrow one as you stated previously. Anything smaller would clog with twigs and muck in no time.

If your sewer pipe is low enough then you could replace the gully with one that has a longer drop then tee the pipe from the aco drain into a 110mm riser pipe between the grid and the u-bend. Then everything is underground and behind the grid, any mucky waste from that pipe won't flow upwards into the aco drain channel...

Alternatively you could put a u-bend directly under the aco drain and tee it directly into the sewage pipe.

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Drain - can I drill the grey area?

Cellophaneskies

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