A. All septic tanks receiving wastewater flows of 750 gallons per day or less shall have a minimum capacity of at least 1,500 gallons of liquid before there will be an overflow into the septic tank outlet. When a housing unit or units served by a septic tank contains more than 5 bedrooms, each bedroom in excess of the 5 shall require an additional 250-gallon increase in the capacity of the septic tank beyond 1,500 gallons. If a septic tank receives wastes from a garbage disposal, the overall capacity of the tank shall be increased by an additional 20% and must include either multiple compartments or multiple tanks;

B. Septic tanks serving premises other than housing units, or receiving wastewater flows of more than 750 gallons per day, but equal to or less than 1,500 gallons per day, shall have a minimum liquid volume capacity to permit retention of incoming sewage at 150% of the average daily flow, but in no case shall the tank capacity be less than 1500 gallons;

C. Septic tanks receiving wastewater flows greater than 1,500 gallons per day shall have a minimum liquid volume capacity (V) equal to at least 1,125 gallons plus 75% of the daily wastewater flow (Q), or V = 1,125 + 0.75Q; and

D. Septic tanks serving premises where high amounts of oil or grease are anticipated shall be preceded by grease interceptors. Wastewater from garbage disposals may not be discharged to grease interceptors. Grease interceptors shall have a grease retention capacity of not less than 2 pounds for each gallon per minute of flow. The minimum size of grease interceptors shall be 750 gallons. Construction and installation of interceptors shall meet the requirements of the Chapter 20:54:06 of the South Dakota State Plumbing Code.