Professional Guide to Sewer Pipe Installation

Planning a new sewer pipe installation can seem like such a challenging task, especially if you’re still learning.

A question that frequently comes up when you're starting a new sewer pipe installation job is how to install sewer lines correctly and what steps go into making sure that everything goes according to plan.

Understanding the process can help break down the difficulties of this job and hopefully make it so that you cause fewer expensive mistakes to either the pipe or the buildings around you. The stakes are high when you're trying to complete a job like this because if they're poorly installed, it can lead to sewage backups, foul odors, and environmental hazards, which could all fall back on you and your team if done incorrectly.

To help you stay ahead of the plumbing trade game and make the most of your time, we’ll break down the key things you’ll need to know about sewer pipe installation, including when a new system is needed, how to choose the right materials, and what the installation process looks like, including calculating the slope (we even recommend a calculator you can buy to make it that much easier).

Before diving right into how sewer installation works, let’s cover when the sewer line will actually need a new drainage system and when it's just a matter of fixing issues. 

In some cases, the issue is obvious—like when you’re building a new home or renovating land around a business—but there are also times when homeowners or businesses are simply unaware that they need an upgraded sewer system.

Below are three common scenarios where a new sewer line installation might be necessary.

Large-scale renovations, particularly if they involve adding a bathroom or reconfiguring a kitchen, often mean that you'll be adding changes to your drainage system. When adding new plumbing fixtures, you’ll need to assess whether your current sewer line can handle the extra flow. Overloading an old system could lead to backups or, worse, a total system failure. Plus, when these projects are done, it's better to replace old and outdated systems at the same time to save time and money. 

When it comes to older homes and even businesses, especially those built before the 1970s, they are likely running on old, outdated sewage pipes, such as clay or cast iron. When it comes down to it, they have long since surpassed their intended lifespan.

These older materials are prone to breaking, collapsing, crumbling, or corroding over time, and as long as they've been buried, they're bound to have tree roots growing into them, making blockages more frequent.

It's also worth noting that poor planning in this critical phase can lead to serious issues down the road. Ensuring the design and installation are done correctly from the start can prevent future headaches like sewer backups, sinkholes, or foundation issues.

We all know that not all sewer pipes are made of the same materials and that choosing the right material for your sewer line installation is an important decision that could make or break the integrity of the system. Factors such as longevity, cost, and resistance to natural elements are what to consider when determining which material is best for your job.

Let’s look at some of the most common sewer pipe materials and their pros and cons.

Installing a new sewer line is a multi-step process, requiring careful planning and precision to ensure the system works effectively. 

Below, we’ll outline the major steps in sewer pipe installation and why each one is important.

Before any digging can begin, the first step in a sewer line installation is planning the entire job out, step-by-step and then determining how deep the pipe needs to be laid. 

The depth of the pipe is one of the most important factors because it helps pipes avoid freezing (in colder climates), as well as ensuring proper drainage once installed. The elevation of the house or business and the slope of the property also feature significant roles in determining the overall pipes depth.

Most professionals will use tools like a laser level or GPS to take precise elevation measurements. These tools make sure that the pipe is sloped correctly from the house to the city sewer tap or septic system.

Ever tried to calculate the slope and realized you aren't quite sure of the formula to get the answer? Well, you're not alone.
 
Finding the proper slope is necessary for any sewer system to function correctly. Sewer lines rely on gravity to move the waste inside of them, and if the slope is off, it can cause a range of different issues with a variety of fixes that aren't so quick to do. 

Too steep, and the wastewater flows too fast, leaving solids behind, which can lead to clogs. 

Too shallow, and the waste won’t flow fast enough, causing slow drainage and, again, possible backups and clogs.

A good rule of thumb for most installations is a 2% slope, or a 2-foot drop for every 100 feet of pipe.

You can calculate the slope by using the following formula:

Slope

=

Total Drop / Total Length of Piper

The ideal range is usually between 1/8 to 1/4 inch per foot of pipe, which allows for a smoother flow inside the pipe system without causing debris build-up. It's better to get it right the first time than to have to come back and fix it. So, make sure to double-check your math by using a calculator.

This is where the Calculated Industries 4095 Pipe Trades Pro - Advanced PipeTrades Math Calc can save you a lot of time. It’s designed to handle a wide range of pipe-related calculations, making sure your slope, offsets, and pressure loss figures are accurate. 

It tackles everything from right angles, offsets, and bends to complex rolling offsets and slope percentage grades. Plus, it handles calculations for flow rates, velocity, force, and volume. 

Whether you're working with clay, cast iron, or plastic pipes, this calculator has built-in data for seven different materials, covering everything from diameter to wall thickness and filled weight per foot.

Need a calculator now? 

Check out Calculated Industries free online calculator below:

Sewer Line Slope Calculator

Once the slope and depth are determined, it's time to start digging. 

The trench needs to be deep enough to allow for the correct pipe slope you calculated but also wide enough to allow for easy pipe installation.

When digging the trench, you should try to minimize soil/dirt disturbance because it can cause the ground to settle once the trench is backfilled, leading to sagging pipes, which in turn can mess up your slope calculations and cause improper drainage.

Sewer pipe installation begins at the lower end of the slope and works its way up. This helps ensure that each section of pipe is properly aligned with the next. 

If you're using bell-and-spigot pipes (which are common in sewer line installation), the bell ends should always face uphill to prevent leaks. This positioning makes sure that any water flowing in the pipe will stay inside, without seeping out through the joints.

For PVC pipes, using a proper PVC primer and glue is needed to create strong, watertight connections. Again, skipping this step or rushing through it can lead to leaks down the road, so it’s worth taking the time to do it right the first time.

After the pipe is installed and inspected, the trench can then be backfilled. Start with a layer of sand or fine gravel to protect the pipe, followed by compacted soil. Compacting the soil as you go helps prevent settling, which we said earlier can cause the sewer pipe to shift or sag over time, leading to drainage issues.

A good practice is to lay a strip of warning tape about a foot or so above the pipe. This tape serves as a visual cue for anyone digging in the area in the future, reducing the risk of accidentally damaging the sewer line during landscaping or other projects.

Sewer lines should be inspected annually, or at least every couple of years, to check for potential problems. Professionals can use camera inspection equipment to look inside the sewer line and spot any early signs of wear, blockages, or other issues. Catching these problems early can save you from the disgusting nightmare of a full-blown sewer backup or pipe failure.

One of the most common problems with sewer pipes, particularly older lines made of clay or cast iron, is tree root intrusion. Roots naturally grow toward sources of water, and a sewer line full of wastewater is essentially an open invitation. Once roots break through the pipe, they can cause blockages, cracks, or even collapse the entire pipe. If you have trees near your sewer line, it’s a good idea to monitor for root growth and remove any problematic roots as soon as they’re detected.

For professionals, sewer pipe installation is more than just laying pipe—it's about precision, planning, and compliance with strict regulations. Proper slope calculations, choosing the right materials, and ensuring correct installation methods are all critical to avoiding costly issues down the line, such as sewage backups or environmental hazards. 

By staying on top of the latest techniques and tools, like advanced pipe calculators, and adhering to industry standards, you ensure a durable, long-lasting system. Regular inspections and proactive maintenance help mitigate risks, keeping your projects running smoothly and your reputation intact.