Selfsufficientish.com

I wouldn't get too bogged down (sorry couldn't resist) about whether it's a septic tank or cesspit as the old-fashioned variety favoured by much of rural Europe (but not the UK) lies somewhere between the two.

Ours leaches liquid into porous limestone while enzymes munch their way happily through all solid matter. It's not needed to be emptied in the 30-years since it was built and we've not noticed any problems since living here for four years. Which brings us back to Milims original question about what is safe to use. I don't think you should put anything down which could stop the bacteria from working. Others prefer to use chemicals but drop a sachet of WC Net, containing concentrated bacteria, http://www.boltongroup.net/pages/Brand_ ... px?bid=120 down the toilet once a week.

Here is another site with lots of septic tank information.
It explains everything about septic tanks from the design to how to look after it, emptying intervals, etc.

I hope you didn't join just to advertise that business Maureen. Please pop into the new members section and introduce yourself and feel free to join in the rest of the forum. If you read our forum rules you'll see we frown upon people joining to advertise and delete their links pronto.