4" Singlewall Internal Perforated End Plug. It is the ideal fitting at the end of a 4" singlewall corrugated drain pipe run. The perforated end cap allows water to slowly percolate back into the soil. Made of high density polyethylene (HDPE), the perforated end plug is designed to last the life of the drainage system. ADS singlewall fittings are the right choice for your residential and commercial drainage projects.