One project is to compare rock and chamber style septic systems used by rural households in Minnesota. We report only the chamber. The goal is to obtain durable trenches of good quality. Two parameters are estimated through Maximum Likelihood Estimate method, namely the minimum amount of flow or load for trench to pool and the amount of load to fill one trench (precisely the difference between the two.) Three kinds of soil are used slow, medium, and fast draining soils. The first parameter agrees for the three draining soils but the second does not. Slow draining soil shows different result compared to the others and contradicts what we expect. To fill one trench, we need more load for slow draining soil rather than for the medium and fast draining soils.