Warning Signs of a Main Sewer Line Clog

warning signs main sewer clog

Many homeowners have dealt with a clogged sink or toilet drain or a slow shower drain. Most of these issues are resolved with simple solutions such as plunging or pouring gunk-dissolving preparations down the drain. These clogs are commonly in the waste system somewhere before the main sewer line and even if a plumber is called, the fix is usually quite affordable.

A main sewer line clog, by contrast, is typically impossible to resolve with DIY remedies. If the clog is due to a crushed portion of the sewer line, you may be facing a costly repair involving backhoe excavation and landscape reconstruction.

So, what are the warning signs of a main sewer line clog and what can you do to prevent it from getting worse? Understanding when a clogged toilet or tub backing up is more than a simple clog can help you take proactive steps and avoid costly repairs.

Here are the main red flags to watch for:

More Than One Backed-Up Drain

Your house has two basic plumbing systems. The lines that bring in fresh water and the lines that carry waste water away from your home. You can think of the waste water system as a tree. The branches are the secondary drain lines that drain from the tubs, sinks and toilets in the various rooms of your house. They flow to the tree trunk – the main waste line – and then out to the street to the municipal sewer line.

Now imagine that the main sewer line (the tree trunk) will not accept waste water from the plumbing fixtures or severely restricts the amount of water it will accept. Fresh water is still being piped into the house and waste water is still trying to drain away. What happens? The water backs up in more than one drain. This is the first indicator that you have a clog in the main sewer line. It is the place that all secondary drains have in common.

If more than one drain is draining slowly, backing up, smells bad or gurgling, your clog is probably located in the main sewer line.

Back-Up in the Sewer Cleanout Pipe

The sewer cleanout is a vertical standing pipe that goes straight down and connects directly to your home’s main sewer line. It was put in place when the plumbing was installed and is required by law. It is usually located right outside the house in line with the sewer line that connects to the municipal sewer. If sewage is draining out of it, or it has standing water in it that smells, the clog is in the sewage line somewhere between that pipe and the street.

Sewage Backup in Floor Drain

Floor drain backup in basements or in the floors of the lower parts of the house, often a laundry room, almost always indicate a sewer line clog. The lower the drain, the closer it may be to the main sewer line. If your house has the misfortune of being built without a sewer line cleanout pipe, this drain may be able to be accessed to clear the obstruction. It may save you the time and expense of having a plumber remove a toilet and use that waste line to clear the clog.

Water Fixture Usage Causes Backups in Other Areas

This telltale symptom of a main sewer ling blockage is often the most distressing. You turn on the sink and the toilet starts to gurgle. You flush your toilet and water backs up into the shower. You run your washing machine and a toilet overflows. These problems indicate that the wastewater that is trying to drain from your house cannot go past the blockage and is being forced back up the line.

Main Sewer Line Clogs Should Be Handled Immediately

If your sewer line is fully clogged, you have no choice but to get it resolved immediately. The fixtures in the house will cease to function properly and sewage backed up into the house is unhealthy.

In most cases, waste pipe blockages build up over time. Partial blockages shouldn’t be managed with methods such as “don’t take a shower while the washing machine is running” because you are only asking for a more serious and expensive plumbing repair down the road. Although it may seem like a catastrophic plumbing problem, partial and full sewer line clogs can be easily, quickly, and affordably resolved with the help of the professional team at Ben Franklin Plumbing.

It’s a Clog in the Main Sewer Line. Now What?

  • Tree roots or stuck waste. In older homes, tree roots are often the cause of main sewer line clogs, especially if the waste pipe is clay. Over time, roots can crack and even crush pipes in their quest for water and minerals. Seismic activity can cause the ground to shift and open cracks in the line that roots enter, causing a clog. Catching a root problem early can prevent the need to excavate and replace all or part of the sewer line. For sewer line clogs, it is advised that you seek professional help. Your sewer line has been compromised and immediate, expert help can reduce a disaster waiting to happen with a simple house call.


The first step is to thread a snake with a spinning weed-eating tip down through the clean-out pipe to chew through the obstruction and clear the line. While roots are often the main culprit, the clog may be an accumulation of roots, waste products or things that went down the toilet that shouldn’t have such as paper towels, or even children’s toys.


  • Broken or crushed sewer line. If your house is over 30 years old, at least part of your sewer line may be nearing the end of its lifetime. Seismic activity in the Bay Area can collapse parts of the line. If snaking the line doesn’t produce results, or the snake hits an obstruction it can’t clear, the next step is to send a camera down to find out what the obstruction is. Often the problem is identified as a massive root or a broken, shifted, or collapsed pipe. Depending upon the location, it may be able to be sectionally repaired with a simple excavation. However, even if the whole line needs to be replaced – the most expensive outcome – you can take heart in the fact that your sewer line will be replaced with modern, long-lasting materials and this expense can adds value to your home.