If your house is not on mains drainage, then it either has to drain into a cesspit, or a septic tank. I am sorry, but occasionally we do have to talk about such things. A cesspit, a brick built tank with a concrete base that collects waste (to be polite, human effluent) and stores it ready for it to be pumped out about twice a year. ( A Somerset cesspit is built with glass beer or cider bottles just below the concrete base, so that when the Building Inspector has approved it, the base is sledge hammered and broken up, so that it does not need regular emptying!) Septic tanks are very different, but are also brick built. They work by anaerobic bacteria breaking up solids into liquids and gases. (Anaerobic bacteria works in an airless situation, which is why every good septic tank has a good 'crust' on it's surface.) As more effluent enters the tank, the excess liquid gently floods into an adjoining tank,for suspended solids to sink to the bottom of the tank and eventually the liquid then discharges into a soak away for any micro organisms to dissolve harmlessly into the ground, where they have been 'neutralised'. There was no crust here so the solids were being washed into the field, and the Environment people were not happy, not happy at all. I patiently explained what I thought was the problem – the lack of a good crust - and said I would write a report to that effect, that could be sent to the Environment Department. Good. But on my way back I was telephoned by my Clients who said they were going to install a new mechanical waste disposal plant...why???   more »