How to Build a Filter for Sewage Drain Overflow

Dig trenches 1 foot wide and 2 feet deep, with 6 feet between each trench. The number of trenches and their length depends on the size of your home, the type of percolation pipes you select, and local soil conditions and building laws. Consult your local government for information about how many feet of trenches you need for your filter system.

Lay about 6 inches of gravel in the bottom of the trench. You need gravel sized between 3/4 inch and 1 1/2 inches in diameter. A quarry will sell you a gravel mix with appropriately sized stones.

Lay your percolation pipes on top of the gravel in the trenches. Keep the holes in the pipe facing toward the bottom of the trench. You can buy percolation pipes at most hardware and building supply stores.

Pour more gravel into the trenches until the percolation pipes are covered by a layer of at least 6 inches.

Spread hay over the gravel that covers the percolation pipes. Place a sheet of plywood over the hay and walk across it to tamp it down. Remove the board and add successive layers of hay until you have a 5-inch layer of hay over the gravel. This prevents dirt from working down between the pieces of gravel and clogging your sewage overflow filter.

Fill the remainder of the trenches in with the dirt you dug out of them. This is called backfilling in the construction business. Place sod or spread grass seed over the trenches. You are ready to connect your septic tank to the sewage drain overflow filter field.