There is no shortage of people who decided to do it themselves and soon discovered these systems simply do not work in heavy clay soils. The state requires a minimum of 750 gallons tank capacity for even the smallest of homes and the disposal field is sized based on home size and also soil quality. Soils are broken into 4 classes: class 1 being sand, class 2 being sandy loam, class 3 being sandy clay loam and class 4 being clay loam. Texas allows these systems to be installed in soils up to class 3 so long as a water table is not present, the higher the soil class present on site the more square feet of disposal field required. Tank sizing is determined by number of bedrooms and square feet of home to ensure proper settling out of solid waste from effluent, if you start getting solid waste into the disposal field your disposal field will soon fail. It is recommended to have your conventional septic tanks cleaned every 3 years to ensure the longest life possible for your disposal field.