And never use the silly blue chemical things that people hang into their toilet cysterns. They distroy the bacteria in the septic tank. Also there should be an overflow of the septic thank which allows the now grey water which comes out of the septic tank to flow into a separate soakway made of cement rings. I have my septic tank now for more than 18 years and had not to pump out anything there. The precleaned grey water goes into one of the cement ring tanks and then I have an additional overflow of that one which goes further down into the garden. This is no problem here, because we are on a slope. So it drains well. We also have quite rocky and sandy soil (unfortunately) that helps to let the grey water soak into it. And if you want to do it really well, you should lead a 1,5" vent pipe from the plastic septic tank up the house wall to roof height and put a T-Fitting on top so the rain can not go down the vent pipe. With this you will not have any bad smell if the weather conditions are not so good.