On the grey water front
Drains may be out of sight and out of mind, but ignore them at your peril! Ian Morris provides a beginner’s guide to French drainage systems
We go down the drains to investigate the murky world of waste water disposal
Most people seem to think that if you can flush the WC and not be troubled by what happens next, the drains must be okay. But this article could be useful if you’re about to buy a house in France – particularly an old property – or if you are troubled by drainage problems in the future.
The basic design of a drain is a series of pipes, properly connected so as to be watertight, laid in a straight line and at a uniform gradient. The gradient is important otherwise nothing goes anywhere. And, depending on location, it might be important to make sure the drain is protected from being crushed – by the weight of vehicles, for example, if it runs under a road.
It would be normal practice, at least in the UK, for inspection chambers to be provided at intervals along a long run of drain, and particularly at those points where the drain changes direction. The inspection chambers, or manholes if you like, are to provide access for drain cleaning rods to be inserted to clear any blockages that might unfortunately occur. This could prove to be important where the drains serve a gîte, or rented property, where guests or tenants don’t think twice about putting disposable nappies and other potentially disastrous items down the drains, irrespective of what you might tell them.
Pipe dreams Sadly, in France, drains rarely live up to the standard described above. Lengths of drain are frequently not straight, and are laid at irregular gradients, encouraging blockages to occur. Individual lengths of drain are often so long between access points that it would not be possible to clear blockages because drainage rods long enough simply don’t exist. And, worst of all, access points or inspection chambers are rarely provided at changes of direction, or at all.
I would estimate that in well over 75% of the properties I have surveyed in France, the drains do not have any inspection points or inspection chambers at all. At best, there is usually an inspection point where the drain from a property runs out across the boundary to join a public sewer. Inspection points in instances such as this invariably consist of a 300mm diameter plastic tube, sometimes extending down more than two metres, such that you can see the drain but cannot physically get to it. All in all, if the stone from your diamond ring is accidentally dropped down the waste pipe while you’re washing your hands, you can pretty much safely say you will never see it again.
Inspection chambers – where they exist – are often poorly made, with no ‘invert’ (the channel pipe that you would expect to run across the bottom of the inspection chamber). The interior of the chamber is often of very rough concrete that you could be excused for thinking had been designed to encourage blockages. Sometimes the inspection chamber is in the form of what I would describe as a ‘catchpit’ where the bottom of the chamber is lower than the inlet and outlet pipes such that it is always full of sewage.
In recent years, drainage inspection chambers (where they exist) have tended to take the form of prefabricated plastic units which at least allow a free flow of waste water. It is rare for any of the features I have identified above to be mentioned in any of the statutory reports that have to be provided by a vendor prior to the sale of a property in France.
Why all the fosse? In my experience the majority of English-speaking buyers are attracted to rural properties, most of which, by virtue of their location, are not connected, and are unlikely ever to be connected, to a public sewer. Properties of this kind have to be provided with their own, or perhaps a shared, drainage disposal installation. And here the term that springs to mind is a fosse septique (septic tank).
It might at this point be worth mentioning the difference between a septic tank and a cesspit. A septic tank is a series of two, or three, interconnected chambers with an inlet at one end and an outlet (at a slightly lower level) at the other end. Bacteria live in the chambers and break down the sewage that passes through; each chamber is in the form of a weir and, thanks to the bacteria, solid matter eventually falls to the bottom in the form of sludge and the liquid element runs out over the top of the weirs and eventually out of the septic tank.
It is vital for the bacteria to be allowed to do their job and for this reason you should never put bleach or other chemicals that could kill the bacteria into drains that connect to a septic tank. Septic tanks do not normally need to be emptied but the sludge that gradually accumulates at the bottom should be pumped out
A septic tank will probably need to connect into an arrangement of perforated pipe drains like this, known as ‘épandage’
Sadly, drainage inspection chambers around older houses in France, where they exist, often look like this