SEWAGE DEPARTMENT TRAINING PROGRAM
How to Build a Free Access Gravity Sandfilter
Install the under drain.
The under drain shall consist of a piece of 4 inch diameter PVC pipe with a minimum 2,500 pound crush test specification.
The length shall be at least 1 foot longer than the internal length of the tank.
Two rows of holes shall be drilled in the pipe. The rows shall be set 45 degrees apart starting 6 inches from one end of the pipe.
The holes will be drilled 6 inches on center along the length of the pipe to a point 18 inches from the other end of the pipe.
