Help please - sewerage connection: what do I need?

[AJB Temple]

I need to connect a new ground floor bathroom with loo, basins, bath and shower to our existing private sewer system (Klargester). This bathroom used to be a kitchen so there is already an underground waste pipe running from a drain outside the window. This is just an ordinary drain that had a small open grill, with waste from the sink and an outside tap above it.

The first picture is the existing drain and the second is the manhole inspection chamber into which it flows. Everything is clear but I know from experience that being able to rod between points can be useful. (Previous owner of this house was an idiot and had fat bergs in the drains).



The drain is set at the moment in a low step or dwarf wall which I can easily remove and rebuild. After some googling I'm not sure what to look for in terms of a drainage chamber to put in. The lavatory pipe and bath outlet will come in from the left, the basins from above and the shower from the right. All just gravitational. Ideally I would also like an open grating for the outside tap - but could live without that if necessary.

Any advice would be appreciated. Especially telling me what to look for on line. If I google man holes something enormous pops up in the searches.

 

[AJB Temple]

Looks like it might be an inspection chamber, but they have no tap grating and all seem to be wide pipe, whereas the sink etc outlets are thin pipe 40 or 44mm maybe. The blue pipe coming out at the moment is redundant and will be removed.

 

[Phil]

Our toilet water goes into a large pipe with breather on the top.
The shower and basin are then just tapped into the pipe.
The only visible pipe above ground is the breather pipe.

 

[Lons]

Adrian

I've been retired a number of years so you would need to check current regs, should be online. You will need building control approval in any case unless things have changed.

You can't / shouldn't just pipe into the existing drain and certainly don't want an open grate over a drain handling sewage unless you want invasive stink.
Usually a soil stack with air admittance valve unless you take it above gutter and window height and branch underground, ideally into the manhole with the new pipe. Handbasin, shower etc. can easily be plumbed into the stack, best way or an open grate but the latter in any event would need a trap installed. Ideally you should have a rodding point on the stack unless it's short when you could remove the valve for access.

Note there are min and max fall allowed for the underground pipe though over a small distance that shouldn't be an issue.

 

[Mike G]

Where are you looking to make the connection into the existing? The easiest is almost always with a new access chamber. The size of the chamber depends on the depth, and the number of connections, and because of a shallow drain run (first photo) and only adding one connection, a 315 shallow access chamber base would seem suitable. You'll need a riser or two to bring it to ground level, and then a lid.

Your connection will have to be vented, but if it isn't the end of the run you can do this with an AAV (air admittance valve, commonly known as a Dirgo). The small connections from hand basins and showers are made into the new vertical section below the AAV, (which has to be above the height of the hand-basin connection). You DON'T connect these small pipes into 110mm pipes in the ground.

PS......your first photo shows an access chamber, and the second shows a trapped gulley, I think.

 

[AJB Temple]

Thank you Mike. I expect I am being a bit dim here. The hope is to replace the little open drain featured in the first photo, with something that will connect directly to the pipe that runs diagonally from the old kitchen into that chamber. The long run that you can see comes from the North side of the house (where you first climbed up the roof) via two other chambers. It's a weird route but of course the building was there before the drains.

I will excavate out the old drain tomorrow and see what the connection needs to be.

There is already an AAV (now I know what it's called) by the Klargester itself. I guess the drain from the old kitchen automatically let air in. There was never any smell even though it connected directly to the sewerage run.

 

[Mike G]

Ah, I follow now. Sorry. That new connection will need to be at an access chamber. Junctions underground are always at access chambers. Forget everything I said about AAVs etc, but the underground stuff, and the access chamber stuff, is what you need to do.

 

[AJB Temple]

OK. Thank you.

 

[AJB Temple]

OK, did a bit of excavating today. The whole lot was fully concreted in, with very flinty concrete, so getting this far took all morning.

There is a buried U-bend, which I was not expecting. Above that is about 4 inches of extension pipe )which I penetrated, annoyingly) into which the drain unit was fitted.

Is it OK to do the sewerage connection from a new inspection / rodding trap into the U-bend? I hope so as it will be a nightmare to get the U bend out. The main pipe that feeds into the big chamber is basically 1" below ground level in this photo, and falls I guess about 18" over a distance of about 5 yards.

The other snag is that the access point (the hole in the photo) is very close to the house wall. Virtually no clearance. I will have to cobble together an offset I suspect.

 

[CHJ]

Don't think it would be wise to connect to the upper side of the Drain U-bend.

Regardless of possible future problems with clearing a blockage you will have a section of waste pipe, in itself needing venting, trapped between two U-bends, and the latter (drain bend) being configured to trap solids rather than ease the flow of such.

 

[AJB Temple]

Hmm. I don't mind installing another vent. The drain in question used to take the flow from the kitchen sink - and flowed freely. I could rod from both ends easily enough because I use a hose type rod attached to a water pressure jet. If waste will clear a lavatory U bend why wouldn't it clear this one as well?

 

[the bear]

The reason you have had no smell coming from that gulley is because of that U bend doing its job. Today you would install either a P trap, universal gulley or bottle gulley to achieve the same. Sounds like you have only had (correctly) liquids going into it above the grill. But these go on drains with open grills and no solids going in. However I have never heard of a U bend on a drain taking solids from a toilet and I suspect there is a reason for that. I can't imagine they would clear the U bend. You need to get rid of the U bend and let the U bend in the toilet do its job. Or "plumb' the toilet in downstream of your existing U bend at a new inspection chamber. If your existing drains have been concreted in I suspect your biggest problem is going to be getting enough off cleanly to get a new connection on without breaking the presumably clay pipe. Been there, and quick dry cement is very good for repairing the clay pipe I guarantee you will damage.

Mark

 

[Lons]

Adrian
You didn't acknowledge my other post so presume it was ignored however I stated that there are minimum & maximum falls permitted for soil waste systems under the regs and I'd suggest that the existing pipe in any case doesn't meet that by quite a long way. Unless my maths are wrong, which of course is quite possible, your pipe has a fall of around 9.5% which is far too much. The reasons are valid to avoid problems with solids waste if you wish to research.

You should be aiming for around 1% to 2.5% ( 1 in 100 minimum to 1 in 40 maximum ). So over the 5 yards you state the pipe should fall by a maximum of 4 1/2".

You need a new soil stack and new pipe into either the existing chamber or preferably a new one. You can easily as already stated vent that and join shower and handbasin pipes to the stack, clean, simple and neat as well as hygenic. You can if you wish retain the existing grate on top of the trapped gully / U bend for drainage under a tap but piped seperately to the soil waste.
A common practice and simple to do. A 5 yard run isn't much excavation. and if as stated you fit an air admittance valve to a short stack then you can rod both ways.

As an ex builder I've laid a lot of drainage.

 

[AJB Temple]

Thank you. I have not measured the fall or the distance - it was just a guess. I'll measure it.

 

[AJB Temple]

I've now read Part H of Building Regs. There is no maximum fall specified. But I do realise that excessive fall may result in separation of solids from liquid. Now that I've actually measured it the fall is about 1 in 48. The outlet in the inspection chamber is not as deep as I had guessed. This appears to be satisfactory.

I'm still pondering the trap. Its primary purpose was obviously to prevent foul gasses emanating from the closed sewer system being emitted by the open grating. My understanding having read about is that U bends are not intended to trap solids as such, but to regulate (slow down) the flow of waste.

With our system we always use a double flush. We have found from experience that this gives the most reliable flow from the system to the Klargester type treatment plant (which is massively oversized for the property).

This particular drain from the former kitchen was very prone to blocking. But that was not a fall issue - it was because the former owners poured cooking fat down the sink (or out of the dishwasher) and solid fat accumulated. That was dealt with long ago when fully cleaned the whole system.

I don't want to dig another drain run as I would have to remove a step and a dwarf wall. However, the drawback with using the present drain is I would have two bends in the pipe from the WC after it leaves the building. I could relocate the WC to put it in a direct line and I could also break into another part of the drainage system (which feeds into the same inspection chamber) by putting the WC on a different wall though that is not an optimal layout. However, if excavation is needed that is much easier digging as in that area there are loose laid slabs.

I'll go to a drainage suppler later on, have a look at fittings availability and talk it over with them. My wife will have opinions on where the WC should go. The other option is a pumped macerator unit I suppose.

 

[Lons]

In that case possibly replace the existing drain with a new system as discussed utilising a stack and connect handbasin and shower as said into the stack, all that assuming you have enough height e.g. not under a window.
I certainly wouldn't be happy with the existing fall and doubt a building inspector would either but replacing gives you the opportunity to reduce the fall if you wanted. The water from shower and basin will help to remove solids which could otherwise end up the same as the cooking fat which blocked previously.

You would lose the grate unless you ran a second pipe, from a new trapped gulley alongside, ideally into the chamber however you might get away with an obtuse or swept Tee into the new pipe very close to the chamber as long as you can get drainage rods into it from there.

All the components are freely available off the shelf at builders merchants and there are catalogues on line, or Screwfix / Toolstation.

 

[Mike G]

.....I've actually measured it the fall is about 1 in 48.......

That really is an issue, Adrian. It's as bad to be too steep as it is to be too fleet. Bob is giving you good advice.

 

[AJB Temple]

Thanks. I will go and have a look at the merchants shortly. I can't do this job for a few weeks I'be now been told as we are solid with garden openings and restaurant bookings, and my wife doesn't want an open trench. Needs to be done before winter though. I think possibly the best solution is to excavate into the drain that is the main straight run into the chamber. This means WC being moved to a different wall probably but that is not the end of the world. The basin and shower can then feed into a new hopper and grating where the pipe is now, as that is just water. That enables me to keep the grating for the tap, although I want something better than what was there before, with the basin and show pipes connect in.

I presume fittings are available that will enable me to T in to the drain run. My wife does not want me to destroy the step or lift the old stone paving in the other run. I think it is better as well to break into the sewerage pipe rather than try to get another one into the brick inspection chamber.

Thanks all for the advice.

BC is not even slightly interested. Just wants photos of the work at each stage. This bathroom project is over a year old as I have been too busy.

 

[AJB Temple]

Just had a look outside again. The drain must go right past the end of the house and should enable me to drop the exit from the WC almost vertically into the pipe. No traps or anything needed and only one bend. Very little digging either. I can fit a piece of pipe with an inspection hatch for rodding (just in case). Should only take a day.

Glad I asked here as it has made me rethink it completely.

 

[AJB Temple]

Having had a chat with BC on the phone and visited a succession of builders merchants it appears the way to do this is excavate, cut out a section of (presumably) clay pipe and fit in a plastic T piece with flexible connectors and then connect the new sewerage pipe into that. Seems straightforward enough. I have bought an angle pipe with a rodding cap for where it comes out of the wall.

 

[Spectric]

Best way to deal with drainage is to dig out until you get to the good pipe and then connect back properly, you do not want to cause blockages. You also do not want unvented dead legs where any fumes cannot pass up a stack which should be before the new soil pipe enters.

 

[AJB Temple]

Well, we excavated through an unexpected 4" concrete slab at the side of the house where the long straight run is and found the pipe 22" deep. We've only exposed a bit but it looks like plastic. Now we need to enlarge the hole enough for me to get a T piece onto the pipe.

 

[Spectric]

Remember these T pieces are not 90°, if you have the right fall on the pipe you are connecting to then the other will be vertical, the same applies if you were to fit the main section vertical then the T off would give you the right fall. Providing access for roding is good forward planing, you never know when freddie and his mates get stuck !

 

[AJB Temple]

This is the pipe. Plastic. To my surprise, underneath it is another pipe at right angles. which I've traced to the stream which runs down the side of our garden and flows into the River Medway. This evidently takes the roof water away.

 

[duke]

Looks like you will be making the connection in a tight hole, hope you have long arms

 

[Spectric]

Also looks like the pipe you need to cut into is clay, used to use a chain type cutter with rollers but now I dare say there are blades designed to do this using a small angle grinder. I would start central to find out how brittle the pipe is so you can make the actual cuts clean.

 

[AJB Temple]

Looks like you will be making the connection in a tight hole, hope you have long arms

It's bigger than it looks. That's nearly a metre of pipe exposed. And I can easily reach down when sat on the edge of the hole.

 

[AJB Temple]

Also looks like the pipe you need to cut into is clay, used to use a chain type cutter with rollers but now I dare say there are blades designed to do this using a small angle grinder. I would start central to find out how brittle the pipe is so you can make the actual cuts clean.

Actually it's plastic pipe. I was expecting clay. It's just a bit muddy that's all. However, I will do a centre cut first as even plastic can be brittle I suppose.

 

[AJB Temple]

In other news I drilled the hole through the wall for the sewerage pipe some months ago. 14cm too high. What a chump. Just had to do it again. Luckily the plug came out intact from the diamond core drill and filled the extraneous hole.