Drainage Materials Fill Material

Any stone sold as drainage fill has been washed and screened so no dust or sand rides along with it. That leaves 30 to 40 percent open space between the pieces, and those voids are what actually move water underground when it rains. Sizes usually run from about 3/8" up to 1-1/2", and the stone is either crushed and angular so it locks together around a pipe, or rounded like river rock when the trench sits right at the surface. What matters more than shape is that the material stays clean — one bucket of fines in the mix and the voids silt up.

Call five different yards and you'll hear the same idea labeled drain rock, #57 stone, 3/4" clean, drainage stone, or Class I backfill. They're all pointing at the same thing: hard rock, washed, no fines, water flows through. It's sold by the cubic yard or by the ton, and pricing sits a notch above driveway gravel because of the extra wash step at the plant. Skip the temptation to save a few bucks by dropping crusher run into a drain trench — the fines pack in, the voids close, and the drain quits inside a season.