Shared Drains - Clarification Please

Joined
22 Sep 2007
Messages
86
Reaction score
7
Location
Northamptonshire
Country
United Kingdom
Hello,
Our Victorian property was built in the year 1900 to 1908 and is situated on a fairy typical UK street of terraced houses. Our particular block of houses consists of five properties of which we are the end (Our properly marked with blue dot). The picture below illustrates perfectly the drainage arrangements.


Needless to say there is no separate arrangements for run off water/sewerage, everything goes down the one drain. Just before the sewers leave the boundary of our property into the main public sewers there is a manhole (see photo)


So my questions are:

1. Why are there two exit pipes into the main street sewer ? If you examine the picture one has white toilet paper in it but there is a second just above it.

2. The bottom exit pipe (one with white toilet paper in it) has a nasty habit of getting blocked on a regular basis. Quite often the bottom trench is full of waste and the top pipe is draining off any liquid. No materials to my knowledge like baby wipes etc are present that could cause a blockage.
Does this happen as now we live in an age of water saving, fewer baths, economy flushing toilets so insufficient water is discharged to remove solid matter ?
Could it be that this happens by design until sufficient back pressure of waste causes it to discharge into the sewer in one big gush ?
Is it more likely that the problem resides on the street sewer where a partial blockage causes this.
Using a hosepipe and drain rods with a large soft rubber disk clears it within 5 minutes (once every 7 to 10 days required).

3. I'm pretty sure that as illustrated in the first picture that unblocking this drain is the responsibility of the water authority (Anglia Water). I resorted to clearing it myself as it was quicker and also if I called them out every fortnight I assumed it would be only a matter of time before they suggested it was in some way the residents faults.
Without a clear understanding of why this is happening I am unsure on how to proceed.

4. The manhole (pictured above) has a badly corroded drain cover which is no longer air tight. If the drain is the responsibility of the water company, is it also their responsibility to replace the cover or is this up to me.

5. How big is the main drain running down the street likely to be that it discharges into. I always imagined it to be something like a 4 to 5 foot high channel you could possibly walk down head stooped. Probably a lot smaller but I really have no idea. If anyone has a diagram that dates this type of property era so I could get a better idea would be great.

Thanks in advance to any 'helpful' posts. If I have missed out any information or additional photos are required please say.

Poisonata
 
Sponsored Links
What you have is called an intercepter trap, they are known for blocking especia;lly on combined rain/foul water systems, they were used to stop the foul air from the sewers so not really needed nowadays, you could ask the water company to remove it, not sure how successful you will be but you never know.
 
That is what is known as an 'Interceptor', basically a 'U' bend in the drain. the top pipe is actually a rodding eye, to allow the section of drain beyond the trap to be rodded out to the main sewer. When the drains were laid there would have been a plug in the top socket to seal it off.

The Victorians had a thing about 'drain air' believing that (rather than the effluent itself) was the cause of their many ills, and the interceptor was fitted to seal the house drains off from the road, thus preventing 'drain air' and rats from entering the house drains. Often a low level vent was fitted on this manhole, with the idea that air could be drawn in here and pulled through the house drains, exiting from the vent stack to ventilate the house drains. The main sewers in the road were fitted with their own cast iron vent stacks.

These interceptors have a habit of blocking on a regular basis, it doesn't take much.... The water and waste should flow through under gravity, but as you've found out, it often doesn't. Keep ringing AW, they should attend, they'll probably jet it which should remove and build up of fat/scale/silt and maybe sort the issue. If not they'll probably investigate further. I'm not sure about the cover, but suspect that may be up to you.

The pipe in the road could be anything from 6" diameter upwards. Nearer you get to the end of the run (i.e. pumping station or the receiving sewage works), the bigger the pipe usually.

Interceptors are still made today, in the rare event anyone wanted to fit one! http://www.knowlesdrainage.co.uk/pr...oryID=12&subcategoryID=20&parentproductID=714
 
First thank you to both of you for posting. This really clears up a lot for me so thank you so much.
Regarding your comments Hugh Jaleak:
Quite often (as the manhole cover is no longer air tight) especially on windy days (this part may be a red herring) a nasty smell emanates from the manhole. On inspection there is no real build up of matter (not that would constitute the level of stink anyway). So potentially as the smell comes from the main street sewer via the top pipe rodding eye as it no longer has a plug ?

The sewer ventilation pipe (cast iron) originally ran up the front of the house (see red arrow)

and joins the manhole (which is situated just in front of the bright blue gate). You can see where it joins the manhole (see grey arrow)


When I inspected the pipe it was in a terrible state of repair and had to be removed. It served no purpose as it was full of rust, 8 feet of the pipe was pipe was packed solid with rust. Whatever happens regarding the blockage I now see that replacing the manhole cover and ventilation pipe needs to happen else the smell will remain.

It is somewhat comforting to know that the likelihood is that the design of the drain rather than anything the residents are doing is the cause. This insight gives me greater confidence when I do finally confront Anglia Water regarding this matter. I suspect like you confirmed a good jet down the second pipe (rod eye) may rectify the problem. The design of the drain is intriguing (thank you for the diagram link) and your observation regarding the Victorians 'drain air' is very interesting.

It is not so difficult resolving issues as I have found over the years once you have a fundamental understanding of their workings.

I will have a think about what to do next. Heaven forbid Anglia Water blame me for the blockage as I had not notified them sooner or the vent pipe (despite the fact it didn't function) is missing.

Thank you very much once again.

Poisonata
 
Sponsored Links
Interceptor trap plug in my manhole has a habit of pushing out of socket by heavy rain/air and fall in trap and block it. I used a wood batten to hold it in.

Daniel.
 
The vent pipe at the manhole (grey arrow) usually led to an early form of air admittance valve (AAV) at ground level, just inside the gate. The vertical stack against the house to act as a vent in this capacity is more uncommon, but reinstatement of the connection between this and the manhole may have benefit. Ventilation of drains is important, blocking off of vents can lead to problems as you have experienced.

Windy days can often cause a change in pressures in drains as the action of the air passing over ventilation stacks acts to draw air up the pipe and thus out of the drains. The original design often was for air passing over the roof level vent to cause a negative pressure inside the drainage system, and air would then enter via the low level vent inside the gate and ventilate the system. The main sewer in the road was sealed off with the water in the interceptor trap and the plug in the rodding eye. Without knowing the full layout it is difficult to imagine the designed intention of your system, but I would think this (now blocked off) vent played its part.

All drains have potential to harbour gases and smells, certain gases I believe attack concrete and metals within the system, possibly hence the corrosion of the cover and cast pipework. I wouldn't worry too much about replacing the rodding eye stopper though, not necessary with modern understanding of drains, they can fall out and cause further problems and there are many thousands of interceptors nationwide without a stopper in the rodding eye! :LOL:
 
So there is definite merit in reinstallation of the vent pipe. Thank you, this makes things very clear.
One further question: As the manhole is fairly sizeable is there any reason I couldn't get down into the hole and rod the interceptor myself all the way to the main street sewer. My only reservation about this was when the rubber disk on the end of the rods reached the street sewer I may have trouble retrieving it back over the lip of the pipe. Or is this better jetted with water for this very reason and/or done by Anglia Water.
 
....... I may have trouble retrieving it back over the lip of the pipe. Or is this better jetted with water for this very reason and/or done by Anglia Water.

I had and probably still have a similar problem- haven't looked down there for a while. I asked similar questions.
My diagram might indicate that there is little improvement in clearing the lower, oft-blocked pipe, as it is so short and joins the upper one almost immediately.

On the matter of over-probing past the exit hole. (and getting your plunger thing stuck) it should be firmly designed and fixed onto the rod. And if you don't ram the muck right through, to the point that you clear the exit, it's probably not a job worth doing, if you see what I mean?
I have pushed stuff all the way through and felt it pop out into the main, perpendicular to ours, at least I knew it was all someone else's problem from that point onwards. You might also clear- for the first time in years the remnants of the vent cover?!
Some comments on my thread also advised about getting the whole antiquated arrangement rebuilt with a simpler design. Not something that I would have a go at, but if you do, post any costs and results?

//www.diynot.com/forums/viewtopic.php?t=393625
 
You can certainly rod the drain if you want but as the water co will deal with any blockages little point.

I also agree you should reinstate the vent.

It might well be adequate to just take it to just above ground level like mine is. You could always extend it further if you really had any bad smells.

Tony
 
The original cast iron vent pipe I removed as it was so badly corroded it was in danger of collapse. Flakes of rust had blocked it totally all the way to the end of its meeting point with the sewer (see above picture - grey arrow).
The ceramic part of the pipe is now clear but I placed a temporary plug where it exits to avoid leaves, muck entering the sewer. There is a small hole in the plug to prevent any build up of positive pressure however this is inadequate for proper ventilation purposes. (see red arrow)



If indeed once the blockage issue is sorted and reinstallation (@Agile Comments) of the pipe is not required (left at ground level) is there a ventilation cover I can purchase (similar to birds nest on toilet stack pipes) that would provide ventilation and prevent entry of debris ?

Thanks in advance,

Poisonata
 
Jetting uses water at high pressure to blast any detritus away, it also has the advantage of be able to go right around the trap and thus clean out any build of of fat, scale etc that may have accumulated. Technically it is Anglian Water's responsibility, (and always has been as the drain was laid prior to the Public Health Act of October 1936), and jetting would provide a superior clean.

I wouldn't recommend going down into the chamber, it is classed as a 'Confined Space' and there is always the danger of noxious gases. Without the correct testing equipment you cannot be sure it is safe to enter.

Regarding ventilation, are there other points further up the drain run where the drain is ventilated, i.e. vent stacks on your neighbours properties? If this is the case I would look at fitting an external AAV (Air admittance Valve) into the existing broken spigot. Fitting an open vent there will just allow foul air and gases to greet you and any visitors outside the front door.... :eek:
 
When systems such as this were installed (and I believe the design continued well into the 1940's), often the low level vent fitted to the manhole at the boundary terminated in a vent using a mica flap inside to act as a 'one way' valve, an early AAV. (Picture in this thread is of a similar item, albeit missing the grille on the front. //www.diynot.com/forums/viewtopic.php?t=240026 )

However the mica flap invariably broke or stuck open, giving anyone in the vicinity a good whiff of 'drain air', sadly never as fragrant as a nearby rose bush! :LOL: (Although as noted, maybe useful for putting off cold callers. Who needs a dog?) Also a good hum from a manhole near the boundary on an older property is often a giveaway for a blocked interceptor too. ;)
 
Mine is similar to that pictured but no mica flap as far as I know but then I have never looked closely at it.

My experience is that when a drain is fully aired and free flowing all the time then it will not smell.

Mine is about 10 m from the front door!

In your case it would seem to have little need IF there is a similar one at the remote end of the run furthest from the road.

Tony
 
Follow Up:

Anglia Water attended surprisingly quickly (within 4 hours of calling) and had the following to say:

1. He suggested to me that it was most likely the reason for the constant blockages was mainly due to the outdated design of the trap exacerbated by the use of water saving measures. I was encouraged to phone them each time it blocked in future as after a threshold of attendances had been reached they would replace the interceptor trap with a straight pipe. He assured me this would rectify the problem and confirmed many other properties on the street had already had this done due to similar problems.

2. The manhole cover he confirmed was the responsibility of Anglia Water and would be replaced by them should the condition deteriorate further.

3. The ventilation pipe he thanked me for removing as it had saved him a job. This is also the responsibility of Anglia Water and he recalled over the last 30 years removing many such pipes completely blocked with rust. However he advised me NOT to replace the pipe as it was no longer required. I mentioned the advice to the contrary, to release any sewer gases that may cause corrosion and/or positive pressure. He assured me the only reason for fitting was to release pressure when the drains were being cleaned prior the modern method of jetting with water. Originally a silo buried at the end of the road would be filled with water then a large sluice gate would be opened releasing all the water. This would flush the main street sewer clean. Any air pressure caused by the sudden rush of water would be released via the vent pipe.

If your having similar problems I would advise contacting your water company straight away as they are responsible for more or less everything (assuming you have a similar sewerage design layout). I did myself a disservice by attending to the problem for well over a year on the false belief it was my responsibility as the drain was within the boundary of my property.

Thank you to everyone who posted in the thread.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top