r area where water had to WASTE PROCESS be added to get it to stop floating, don't have the entire contents pumped out or the tank may float again, breaking the inlet and outlet pipes. DOSING CHAMBERS Application There is evidence that alternating periods of saturation and rest- ing are preferable to continuous discharge into a drain field. A period of drying allows the soil to re-aerate, limiting the thickness of the biological mat and allowing aerobic digestion of filtered organic particles. To achieve this periodic wetting and drying, a dosing chamber is used. Dosing under pressure provides equal distribution of effluent to the entire drain field, reducing the overloading of areas under sags in the distribution pipe. A dosing chamber is necessary under three conditions: if the eleva- tion of the drain field is such that effluent from the septic tank cannot drain into it by gravity flow; if the drain field is designed to utilize a pressure distribution system; and if the drain field distribu- tion pipe exceeds about 500 linear ft. The same dosing chamber design can serve all three functions, although design is most critical when combined with a pressure distribution system. One type of dosing chamber (Figure 4.6) consists of a pump and a tank separate from the septic tank (although a chamber can be built directly onto the end of a septic tank). Note: A dosing pump should never be located inside the septic tank, as solid materials would be pumped into the drain field. Under conditions where the elevation of the disposal field is 2 to 5 ft or more below that of the septic tank, it may be possible to use an automatic dosing siphon in place of a pump (Figure 4.7). Their use is generally restricted to applications where conventional 4-in. perfo- rated drain pipe is used. Alternating dosing siphons for distributing effluent to multiple drain fields in sequence are available. Two dos- ing siphons in the same tank at the same depth and discharge level will alternate. Where they can be used, siphons are preferable to pu