MOST septic tanks in France are of the type known as toutes eaux, in other words, they take all the grey water from the kitchen and bathroom, as well as sewage from the lavatory writes Patricia Mansfield-Devine.
The main thing to remember about the system is that it is 'live' - it's a living organism, so, as all septic tank users become aware very quickly, you have to be very careful about cleaning products.
Managing the tank
Use only toilet paper and cleaning products that specifically say 'sans danger pour fosses septiques' on the pack (it's usually on the back). There aren't as many of these as there used to be, but there are still plenty to be found, such as most of the Canard WC (Toilet Duck) range.
Septic-tank-safe toilet paper can be found in any supermarket. It looks the same as ordinary toilet roll, but tends to be thinner than the high-end padded varieties that are now common in the UK and should contain no perfume, though it sometimes contains dyestuffs.
You absolutely cannot flush moist toilet paper, baby wipes or sanitary products down a septic tank because they are not biodegradable - use disposal bags and a pedal bin instead for this kind of product and make sure there's a notice above the loo if you have guests in your house. Don't use too much toilet roll, either, and ask your guests to be a bit sparing (otherwise visitors seem to get through reams of toilet paper in short order and this can choke the tank...).
Never rinse any product containing bleach (eau Javel) down the toilet, bath or sink, and make sure you check existing product labels regularly. Brands are changing their ingredients as more people in the countryside move to town drainage and the Ajax range, for instance, isn't as safe as it was ten years ago.
You can use small amounts of bleach in your sinks, etc, by being very careful. Put the plug in, wipe round the sink with an eggcup full of bleach and leave it overnight to 'go off' before rinsing fully in the morning. That way you get maximum cleaning power without killing off the septic tank.
You cannot use disinfectants of the Dettol type at all in sinks, baths or toilets, and in any case they seem to be in short supply in France. Instead, you may find cleaning alcohol useful for cleaning the toilet seat and lid, taps, etc.
Cleaning alcohol comes in two types - alcohol à bruler, which comes in 5-litre bottles and is unscented, and the more expensive alcohol à menager, which comes in a litre bottle and with added perfumes such as lemon and vanilla. Transfer either type to a clearly labelled spray bottle, spritz down your toilet seat and lid, and wipe it dry with kitchen roll, which can then go in the waste bin. Don't use sponges which then have to be rinsed into the drainage system.
Cleaning alcohol can be used for all sorts of things, including white goods such as fridges and difficult-to-clean objects like coffeemakers and metal kettles.
For cleaning sinks and baths, and also unclogging smelly pipes, you could try good old-fashioned washing soda. This is better than constantly using residue cleaners such as Cif (Jif in the UK). Washing soda is called Cristaux de soude in French, and there is a brand called Marc which produces 'lessive au resin du pin', which has pine oil added (the pine oil is good for the floor, but not the septic tank, so don't flush this particular variety).
Make sure to wear rubber gloves when using washing soda, as it will take your skin off, but if you've never used it before, you'll be surprised at how it cuts right through grease - it's perfect for windows, the floor, the cooker etc.
For simultaneously cleaning and freshening up floors and walls, you can use any of the common bactericidal floor cleaners, but pour these outside on the garden, not down the sink. For cleaning kitchen work surfaces, use either unscented cleaning alcohol or white vinegar, again using kitchen paper to mop up the excess.
If you run a dishwasher, buy powder, not tablets, and only fill the reservoir half full - you really don't need as much product as there is in a tablet and it only clogs up the machine anyway. Do the same with your washing machine - choose liquid wash where possible, and avoid anything that contains bleach. K2R stain remover seems to be safe with a septic tank if you have stubborn stains you need to remove.
If you do need to bleach your washing, buy eau javel tablets, which measure out a careful dose - one or two a week is said to be safe in the septic tank. Nevertheless, it's still safer to bleach clothes in a bucket for 20 minutes and then transfer the washing to the machine.
Feeding the tank
Eparcyl is a septic tank feeder containing yeasts and bacteria that keep the tank alive. It's useful if you have a holiday home, but you may not really need it if the tank is used quite often (such as if you live in your French home full time). Just open a sachet, shake the powder into the toilet bowl and flush.
Flushing meat and veg down the loo is also recommended by some people - the theory being that it gives the tank something to feed on.
If you kill the tank
If you accidentally kill off the tank, you can buy a complete restarter kit from DIY shops. It's not generally available in supermarkets. However, with careful management, this should not be necessary.
Patricia Mansfield-Devine is a freelance journalist and editor, to read more about her life in France please visit Montcocher.