drainage query

[Steve]

I am undertaking some work in the garden, part of which is digging up the concrete around the manhole cover and then laying turf. I may also replace the manhole cover with an infill one to grow turf in it.

I lifted the manhole cover up just out of curiosity and found that there's standing water in there. If I remember correctly this was also the case a few years ago when I moved in, but I thought nothing of it.

Is this normal / correct? I thought the water should drain away freely, not stopping on its way to the main sewer. Currently, the red arrow shows where the water enters this chamber, the end of that inlet is underwater. The blue arrow shows the old inlet from the toilet in the adjacent coalhouse. The toilet is no longer there and the drain has been concreted over.

The purple arrow shows the outlet, though at the moment all the water (etc) flows over that angled pipe - about 45 degrees. It looks like there is another pipe outlet below the angled one, but its submerged and I cant tell if it goes anywhere. If anything it looks like the 45 degrees pipe would "foul" any outlet pipe below it.

Any advice?

Untitled

• Steve
• 1 May 2013
• 1

(I posted this in building because as I understand it, builders do underground drains. Moderators feel free to move this if you feel its in the wrong place.)

 

[pinenot]

Normally manholes are free of standing liquid and the inlets are above or level with the outlet, level as in incorporating the run. The angle of the outlet could simply be an adjustment in drain levels i.e. from house(s) to main sewer. If it was anything else, then without an inspection hatch, it would just be wrong. That aside there's no absolute problem with the configuration as it is, but suggests the manhole may have been possibly an after build??

The manhole, although surrounded by brick, doesn't look like it is brick build, how therefore are you intending to lower the top of it, or is there a dropped insert cover that will allow a growing depth??...pinenot

 

[kbdiy]

That looks to me like the trap could be blocked and the waste is flowing over through the rodding eye. As the trap is blocked you have standing waste water covering the channel and benching up to the level of the rodding eye. Can you tell how deep the standing water is? I can't see any sign of the channel through the muck.

Something like this: //www.diynot.com/network/kbdiy/albums/16249/60778

Time to get the rods out methinks

 

[Hugh Jaleak]

Have a look at the link, kbdiy has it sussed, you've a blocked interceptor trap there. Need a couple of rods and 4" plunger disc, make sure they're tightly screwed together before using though!

Under that open rodding eye is the interceptor inlet, it's blocked up. Few good plunges (careful you dont splash yourself!) and it should clear. There'll be a fair bit of waste possibly backed up the pipes, wont be very pleasant but flush copious quantities of water through and it should start to smell a bit sweeter.

The inlet you'll find is somewhat lower, it then goes in a gentle 'U' shape back up to the outlet. The open pipe you can currently see connect to the far side of the 'U', to allow for rodding the section past the trap to the main sewer. When fitted the rodding eye would have been fitted with a stopper, more often than not these have been removed over the years, so when the trap blocks (these are prone to blocking....), the effluent simply flows away through the rodding eye. Problem is then solid matter can build up in the (now full) pipework, eventually causing a blockage upstream.

 

[Steve]

Thanks everyone.

Whats the point of these ere interceptors then? Why do I have one?

I think my dad has some rods. I'll ask him.

 

[pinenot]

Interceptors

Interceptors are often placed on drain lines to protect the downstream environment from possible pollutants. Most commonly interceptors are used for separating out silts and hydrocarbons (oils and fuels).

 

[Steve]

http://www.diyinfozone.com/blocked-drains-problem-solving

Looking at the explanation here, it mentions that the stopper might have fallen into the trap. I hope this isnt the case and its just a normal blockage. At least I know what it looks like now.

These interceptors looks like they might cause problems with modern toilets. They look like they were designed with having 12 litres of water being flushed through with the solids to clear the trap each time. One cant help but think 3 litres might leave all the solids in the trap . . .

 

[Hugh Jaleak]

That type of interceptor in your link Steve dates from the Victorian era. Our ancestors did realise the link between poor sanitation and poor health, however initially I believe they were convinced it was drain air that was the cause of their ills, rather than the actual effluent itself and the rats that lived in it.....

As part of this interceptor traps were designed, and were fitted on connections from house drain to the sewer. Usually a low level vent was also fitted from the last manhole containing the interceptor. Idea being, the interceptor prevented sewer gases (and rats etc) escaping from the main sewer into the house drains. Then, with air being drawn over the top of the soil stack up the the side of the property, this would then draw air into the house drainage via the low level vent, through the drains and out the stack, thus ventilating the house drainage system.

These interceptors have always been prone to blocking, to overcome this a they were made with a sharp weir inlet and a gradual outlet to aid flow. A complete stopper is unlikely to fit in the interceptor, may be sitting over the top (if its even still there...), but bits of broken masonry or pipe can soon cause problems. Try the plunger first, if this doesnt work then try a corkscrew attachment, see if this will loosen the detritus in the trap.

The new 3/6 litre flushes may not may ideal for these traps, but with the additional flow through on a daily basis from showers, dishwashers, washing machines etc, (coupled with the fact a lot of homes of that era also discharge rainwater into the foul sewer) then there should be enough throughput to keep the interceptor clear.

 

[Steve]

If it isn't strictly required its tempting me to dig it out. As far as I know this manhole only serves my soil stack, that's it. No other houses, no other drains. But its a lot of work for very little gain.

 

[noseall]

Bite the bullet and dig it out lad.

Do it right and do it once, then put the lid back and forget about the drains.