S.C. Code Ann. § 44-55-630

The plans for each septic tank having a capacity of one thousand gallons or more shall have the approval of the county health officer before the tank is installed. Each such tank shall have a second or effluent compartment not longer than one third the total length of the tank nor shorter than three feet and shall be equipped with a dosing chamber and siphon if a tile field or filter is used for secondary treatment of the tank effluent.