53 Pa. Stat. § 4617
Where subsoil drains are placed under the cellar floor or used to encircle the outer walls of a building, the same shall be made of open-jointed drain tile or vitrified clay pipe, and shall be effectively trapped before connecting into the building drain or building sewer, or shall connect into the storm water drain inside the storm water trap. The pipe must be laid on no less than four inches and covered with no less than six inches of crushed stone or gravel of medium size, and arrangements made to cover the stone with a material to prevent, as much as possible, sand or dirt from washing into and clogging the stone or gravel bed and cover. Where danger of basement flooding exists, they shall be protected against back-pressure by an automatic back-pressure valve, accessibly located, before entering the building sewer or drain, or they may discharge through a cellar floor drain provided with a backwater valve.
53 P.S. § 4617