Advice on garden drain run please.

chubsta

Have an issue with a sewery-smell coming from our drains and want to make sure I am not going to have to waste money if I don't have too...

Drains naturally run from the house, along under the garden path and out of the garden about 20 meters away, just before it exits the garden there is a large inspection hatch.

We did have a blockage a month or so ago where the water was backing up from the inspection site back towards the house but it turns out that was because the lower 'exit' in the pipe (see phot below) from the inspection hatch was blocked with grit etc (probably hadn't been cleared in forever), this meant that waste was sitting in the pipe - anyway, all fixed with a good cleaning out.

Thing is we are still getting a horrible smell from that end of the garden usually in the region of the inspection hatch - everything is flowing through easily from the house, so all I can think of is that it its coming up from the main sewer.

Looking at the exit pipe from the inspection hatch I see this:



The waste goes out through the lower pipe, which appears to be some form of S-bend and then it joins the main pipe above. Im guessing because the main hole is just a straight drop to the main sewer that that is where the smell comes from so should it have some sort of cover on it at all, or be in some way blocked so gas can't come up? When we had our blockage it was the lower pipe that was blocked so the fact the upper one was open meant the waste ended up flowing out through there so the inspection hole didn't fill up beyond the lip of the lower pipe so it worked for us from that point of view but it seems strange there would be a lower pipe with a water barrier but an open pipe above!

Any and all advice appreciated!!

stuart45

It's an interceptor trap, which used to have a plug for the top, but like most have long been lost. They aren't used in modern drainage systems because of the issues of blockages.

Section62

stuart45 said:

It's an interceptor trap, which used to have a plug for the top, but like most have long been lost. They aren't used in modern drainage systems because of the issues of blockages.

^This.

Bad smells from sewers usually indicate a blockage somewhere - most of the water in foul sewers is from baths, showers, sinks, washing machines etc so typically has a floral/detergent smell.  Bad smells generally come from the solids as they undergo anaerobic decomposition, which in drains and sewers should only happen when there is a blockage somewhere.

The idea of an interceptor trap was to prevent 'bad air' from entering the property's drainage from the main drainage system. The plug that goes in the top hole stops air entering the chamber from the main sewer, whilst allowing the downstream drain to be rodded out. Interceptors are prone to blockage, not least if the plug falls out and blocks the 'u'-bend, or in some cases gets into the downstream pipe.

I would suspect the source of the bad smell is either from a blockage further downstream, or else from decomposing 'solids' which have been left in one of the pipes (or on the benching of a chamber) before the interceptor blockage was cleared.

The amount of smell also depends on how well the chamber cover seals.  The cheat way of dealing with smells coming from a chamber is to replace the cover with one that seals better.

Eldi_Dos

If you are sure all the drains are running freely try sealing the chamber cover.

Lift off and put lid upside down then with a stiff wire brush clear and clean the frame and area of lid that is going to sit inside frame, lagger both areas with grease, you could, but most do not, put a natural fibre cord in frame and grease that, before replacing lid.

chubsta

I'm pretty happy our drains are fine, they have been rodded fully and when we do a test flush everything appears as it should - the run is long and shallow from the house to the inspection hatch but a game of poo-sticks is possible!

The smell isn't 'that' strong, you just get a whiff much of the time at that end of the garden and it isn't really an 'excrement' smell, it is just that one I always associate with sewers so will try to seal the cover as a first step I think - thanks for all the advice!

Eldi_Dos

If you are putting solids from a litter tray down the wc that could be how grit is getting introduced into the system.

chubsta

Eldi_Dos said:

If you are putting solids from a litter tray down the wc that could be how grit is getting introduced into the system.

Nothing like that going in, the grit I mentioned is just stuff that naturally gets into a pipe system over decades and sinks to the bottom of the s-bend part in the exit drain. As it has now all been cleared I envisage it taking a few more decades to be an issue again!