Summary: Use these methods to install large drainage inlets, or vertical structures, on drain lines.
The first section of this post will discuss the installation of a 24″ inlet, or manhole, on a live 12″ PVC drain line with 4″ of water running in the pipe.
I use drainage inlets made of solid, double wall HDPE pipe. After installing a metal plate on the bottom, I cut pipe hole inverts one foot above the plate; this creates a sediment basin. Water-borne debris will fall into the basin before entering the outfall pipe.
After we excavated a 48″ hole around the new inlet location, we excavated 18 inches below the pipe invert to allow for 6 ” of crushed stone and the 12″ basin below the pipe invert. After excavating the work limit, a laborer walked over with a beach ball. Twenty feet away, the laborer found an existing drain inlet connected to the same 12″ drain line. He blocked the discharge end with the beach ball. The water stopped at the new inlet location.
We cut and removed 22″ of the live drain line, centered on the designed grate location. This measurement is important; the 22″ measurement allows for installation of the inlet while providing a few inch overhang for the horizontal pipe. The 12″ holes were cut an inch wide, and we cut a 45 degree bevel on the inside of the 12″ holes. The inlet slipped on the drain pipe opening with a gentle nudge. Another method involves a bell-end coupling. Cut a 4 foot section of pipe on the existing line and replace it with a bell-end coupler after installing the inlet.
I”ve had a few bad experiences with flimsy 24″ inlet covers made of welded wire. This installation used a light duty frame-and-grate sold by a waterworks company. These structures won’t fit into the 24″ pipe; they rest on the inlet top. Install concrete along the frame edge to insure stability.
We removed the beach ball, and the water flowed into the new inlet. We donated the beach ball to the young daughter of the laborer.