What it is
100-foot coil of 4-inch black HDPE drain pipe, slotted along the length so water can enter the pipe through the perfs. Sometimes called a "slotted pipe" or "leach pipe." Lightweight, flexible, coils to a manageable size for transport.
What it's for
The pipe that goes in the bottom of a French drain. Water seeps through the surrounding drain rock, enters the pipe through the slots, and flows downhill to daylight (or a curb cutout, or a sump). Without this pipe, you have a rock-filled trench that holds some water — not a drain.
Common uses:
- French drains along a foundation — captures water before it gets under the house.
- Yard drains in low spots — that one place in the back yard that's a swamp three days after rain.
- Downspout extensions — buried collection from downspouts to carry roof water to the curb.
- Behind retaining walls — keeps hydrostatic pressure off the back of the wall.
French drain build, top to bottom
The standard layered build:
- Dig a trench, sloped 1% (about 1" of drop per 8 feet of run) toward the outflow.
- Line the trench with woven landscape fabric. Big enough flap on both sides to wrap over the top later.
- Lay 2" of drain rock in the bottom.
- Set the perforated pipe on the rock. Slots facing DOWN — counterintuitive, but this is how it's spec'd. Water enters from the rock below; if slots face up, the pipe takes too long to fill and water backs up.
- Surround the pipe with more drain rock to within 4-6" of grade.
- Wrap the fabric flaps over the top of the rock to seal it.
- Backfill with topsoil or sod.
The outflow end connects to solid drain pipe — un-slotted — that carries the water to where you want it to come out.
How much do I need
One 100-foot coil covers most residential drain runs. For longer runs, buy multiple coils — they connect with standard 4" couplers (not included; pick up at the yard counter).
| Drain length | Coils needed |
|---|---|
| Under 100 LF | 1 |
| 200 LF | 2 |
| 300 LF | 3 |
Use the french-drain wizard — enter trench dimensions and we'll spec drain rock, pipe, and filter fabric in one bundle.
Buying tips
- Slots face down. Write it on the pipe with a Sharpie if you're going to lay the coil over a weekend — easy to forget which way is which when you're in the trench.
- Couplers are sold separately ($2-3 each).
- For drains under a driveway, use solid pipe instead of perforated — you don't want water entering the pipe under a slab.
Contractor notes
Bundle quotes for French-drain installs available — pipe + drain rock + filter fabric pre-priced at contractor terms.
In the field
