Abstract: A combination of a biological dry toilet and a biological waste water purifying plant. In the combination the heat and coarse sludge of the so called grey water from households is recovered in the dry toilet to which also the fine sludge from the waste water purifying plant is pumped. The heat obtained is used for heating the compost and both sludges collected in the filters are from time to time combined to compost them together with the other waste in the dry toilet. A suction fan in the dry toilet also sucks the air needed by the biofilter through the filter bed. The purified water obtained from the waste water purifying plant is absorbed in the soil.