Drain Pipe Digging

Table of Contents

The purpose of an outdoor drain pipe system (sometimes called a “French drain”) is to accelerate the movement of water or to intercept and redirect sub-surface water. This is accomplished by installing gravel covered perforated drainage pipes in narrow trenches. Such drain pipes can prevent basement or crawlspace flooding and dry out the soil surrounding a house.


The materials needed are few and simple: piping, gravel, and filter fabric.


A French drain is typically piped with rigid PVC plastic drain piping with perforations along one side of the pipe. Usually, a 4-inch pipe is used. This pipe is preferable to corrugated drainage pipe, which can be hard to clean with a Roto-Rooter. The older clay or ceramic pipe is no longer used.

Filter fabric

Filter fabric is used to line the trench to prevent earth and fine material from traveling through the gravel and eventually clogging the system.


Filling and finishing materials

The trench is filled with washed gravel of about 1-inch diameter, and the trench is topped with one of sod or flagstones, in most cases.



Location depends in large part on the purpose of the drain pipe. Whatever the purpose, the first step is to check that your digging will not damage existing underground infrastructure, such as pipes, electrical conduits, or cable TV or telephone wiring. Also, ensure that your work will conform to municipal building codes and by-laws. Dealing with red tape is a nuisance, but the consequences of not having the required permissions are usually much worse.

If you are intending to have the drain pipe keep a basement dry, install the pipe about 4 to 6 feet from the foundation of the house.

If your yard is nearly level and the purpose of the piping system is to drain standing water, you will probably have to dig a series of trenches and inter-connect them.

Whatever the purpose, remember that roots are a major enemy of underground piping, and locate the piping system away from plant life whose roots could penetrate the system. Also, when possible, consider routing away from property lines or neighboring properties.


Once the project has the all clear to dig, the drain pipe trench is dug approximately 6 inches wide and approximately 24 inches deep.

Create the trench starting along the highest part of your property, and extending to the lowest part of your yard. This routing will ensure the slope of the pipe will be sufficient to carry away water in the drain pipe.

A builder’s level obtained from a tool rental store will help you determine where and how deep to dig the trenches.

Even properties that appear flat often have the slope needed to install the pipes so that they will extend to daylight at the lowest portion of your yard. A one percent grade is sufficient to move water through the system.

Once the trench is dug, it is important to compact any loose soil in the bottom of the trench. If the trench network is not extensive, compacting can be done manually with a four-foot length of 6″ by 6″ wooden beam.


At this point, the trench should be lined with filter fabric before adding the first gravel. The filter fabric will ensure that the pipe does not get blocked by large pieces of debris being washed into it.

Then, install a 1 or 2-inch layer of washed gravel on top of the compacted soil before you lay down the perforated piping. Do NOT place the piping directly on the soil, because the drainage holes in the pipe, through which water will enter, need to be up above the soil.

The drain pipe itself is installed with its holes facing downward. This placement ensures that water enters the pipe sooner than if the holes pointed up. Moreover,holes that point up are perfect targets to get clogged with the rounded gravel that will be used to fill the trench.

After the pipe is installed in the trench, cover it with 1 inch or larger washed, rounded gravel. Fill the trench with gravel to within 1 inch of the surface. Place a piece of sod over the gravel to disguise the trench.

If you wish to control surface water that flows over your lot, allow the gravel to extend completely to the surface.


Sections of drain piping are best connected with fittings that will allow a snake or Roto-Rooter to navigate the connections. For corners, rather than using 90-degree elbows, use either a long 90-degree connection or two 45 degree connections with a short straight segment between them. At “T” junctions, it is best to use a 45 degree “Y” connection paired with a 45-degree connection.

For a complete and professional drain pipe installation, contact Master Drain today.

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