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How drain lines work

This graphic shows the basic paths of a typical home's drain line and sewer plumbing — key parts of which carry no water at all, but only air to provide proper venting.

1: All drain pipes should be connected to a network of ventilation pipes that go up through the roof. Venting prevents sewer gases from drifting out of drains into living quarters.

Experts say it's a good idea to inspect a sewer line with a camera before you purchase a home. During the inspection, make sure the inspector confirms that all venting pipes are present.

2: Most plumbing fixtures have curved "trap" sections that hold a little water, forming an airtight seal to keep gases in. This section of pipe is easily removed to clear clogs.

3: Toilets also have a trap, which is what keeps standing water in the bowl. The toilet drain is the largest drain pipe in the house.

4: All household drains meet below the house in a main drain that carries the wastewater to the municipal sewer lines or to a septic system. A Y-shaped pipe in a basement or crawlspace provides clean-out access.

Sanitary vs. storm sewers

There are two types of sewer systems: storm water systems and sanitary sewers. Storm water systems or drains carry rainwater, ground water and road runoff water to an open body of water, such as streams, lakes and oceans. Sanitary sewers, however, carry wastewater from residential and commercial buildings to a treatment plant where the contaminants in the water can be removed.

Since the 1930s, storm drains and sanitary drains have been installed separately to prevent cross contamination. In a residence, the home's drain system is connected to the city sewer by an underground pipe called a lateral line, usually 4 to 6 inches in diameter, installed at a slope to use gravity for water flow.

The size of the home's drain piping is determined by the amount of flow possible and the type of waste material anticipated. For example, a bathroom sink usually has low volume and little if any solids in the water. These pipes are normally 1 ¼ inches in diameter. Bathtub, washing machine and kitchen sink drains carry larger volumes, with food and other solids possible in the kitchen sink. Therefore, a larger diameter pipe is necessary, usually 1 ½ inches in diameter.

Any plumbing beneath the house is large enough to accept the flow from the fixture drains. A 2-inch diameter pipe is common. All of these drains flow into the toilet drain to exit the building, so the toilet drain is the largest and matches the lateral line going to the city sewer system.

Drain clogs

Homeowners can often fix drain clogs themselves if the problem is confined to specific fixtures such as a sink drain or a toilet. However, when all drains are affected — or when you see warning signs, such as water going down one drain and backing up in another — that generally means the main drain is clogged. Call a plumber who specializes in clearing drains.

If it’s a blockage from something flushed down a toilet, clear the drain by using a plumber’s auger or snake. However, in older neighborhoods, the cause may be tree roots. Older sewer lines were made from fired clay and as they age and weaken the tree roots creep in.

Drain experts are often able to bore through the roots and clear the drain, but in many cases the original drain pipe has become so deteriorated that the new passageway eventually collapses. When this happens the drain line usually needs to be replaced.

When lines become clogged and damages occur, in the majority of cases, the homeowners’ responsibility begins at the connection point to the city sewer system and includes the lateral lines and all drain plumbing in the home. Any maintenance, repairs and unclogging of these lines must be done by the homeowner, often with the help of a plumbing service.

While the indoor piping is relatively easy to repair, underground lateral lines require specialized equipment and tools, so those repairs often require a plumber.

Trenchless sewer lines

If a sewer line springs a leak or is punctured and in need of repair, it can create a mess for the homeowner and plumber. Certain professionals opt for trenchless sewer repairs, a technology that requires little digging and is gaining popularity.

The process uses a fiberglass tube coated with epoxy resin that's inserted into the damaged pipe and blown up like a balloon. After a few hours, the epoxy hardens and creates a pipe within a pipe.

Trenchless options can cost 30 to 50 percent more than conventional digging, so if the ground above is just grass it would probably make more financial sense to dig a traditional trench and re-sod afterward. However, the trenchless method is worth the cost when obstructions such as decks and stone patios have been built over the path of the sewer line.

Avoiding sewer clogs

Homeowners can reduce the risk of drain clogs by being careful what they put down the drains in the house. Don't flush items like cotton swabs, gauze, tampons, maxi pads, diapers, paper towels and heavier materials because those materials aren't designed to break down easily.

Many plumbers say “flushable” wipes don’t really degrade well enough to be put down the toilet.

Other materials that can create problems include paint, oil, grease-based products or harsh chemicals — even chemicals designed to prevent clogs. They may go down the toilet with seeming ease, but that doesn't mean they won't cause problems farther down the line.

Because sewer repairs often fall under the individual homeowner's responsibility, preventive maintenance could end up saving thousands of dollars in potential damages. These five tips can help homeowners keep sewer pipes flowing freely:

• Inspect in advance: If you’re thinking of purchasing a home, add a sewer pipe inspection to your checklist of considerations before buying.

• Consider a video viewing: Have a professional examine your pipe with a camera to determine its condition. Then you can budget for repairs or replacement that may be needed down the line.

• Rout it out: If roots are already finding their way into your sewer lateral, you might buy some time before the next backup by having them cleared.

• Consider coverage: The majority of homeowners' insurance policies won't pay for sewer pipe replacement; however, you might find one that does if you shop around.

• Do your research: Before an emergency arises, talk to your plumber about whether a trenchless or traditional method of sewer pipe replacement might be right for your home. Keep this potential repair in mind when spending on landscaping or hardscaping that might be affected.

Leave a Comment - 15


Natalie Zadeh


We have a clogged sewer line. We paid $350 to a company to use a camera to see what is going on . He could go all the way through the pipe and gets stopped close to the street. We have brought couple of other plumbers most of them recommend replacing all the piping as it's an old house . The estimates are around $9000 to $14000 which is a lot! Is this that the right number? Is there any other solution?
Thank you!

Marie reilly


I have occasional sewage back ups only in my downstairs utility room and bathroom areas. They might be coinciding with super high tides. I live in Mia Bch. The plumber that comes out to help at those times says it may have to do with the city and or I need to have a two-way clean out installed. What is that and what do you think?

Thanks for any help in knowing what to do to deal with this without spending money that I may not have to!



What would be a ball-park cost to replace approx 70' of old clay sewer line that has root invasion?

Thank you.



I called a plumber to come look at my clogged rain water lines from the house to the street. To clean out one and look at the other, only 3 feet in from the street, he charged me $442.00 for one hour. Said the camera and equipment is expensive, so that's why it cost so much. i think i was overcharged, especially after reading the above post.

Bryan Smith


For avoiding pipe clogging Pipe bonding with proper sealant is also important otherwise roots of the trees will enter in sewer lines through it. Parson adhesives are also quality supplier of the adhesives and sealant recommended by worlds leading manufacturing companies.



Prev. Owner broke cap off vert sewer line. Is cap supposed to be solid cover hat allows venting around edges or is it a vented cap with holes? Or does it matter? Ground level or higher?

sewer & drain...that's the name


The cap on your sewer line should be left loose or flipped upside down to allow a "backup" to come out at this area instead of inside of the house . The pipe is vented from the roof (you can see the pipes sticking up out of the roof).

Barbara Baass


I had a clogged sewer line and had a plumber with a camera look at it. Cost was $150 and he marked it with an X where the stoppage was. I called another plumber & he dug it up with a shovel & replaced 4ft. of pipe for $450 & it didn't even take him two hours. It was split & full of roots.



The estimate I received is very costly to replace my sewer line from the street to the house, I was told about a new technic sort of like the trench less, whereas a pipe or tube is snake through the old pipe and takes the place where the crack was or is. Does anyone have any information on a procedure such as this; I would greatly appreciate the information, thanks...

Satellite Steve Johnson


Aside from keeping the sewer carrying pee and poop, toilet paper is the only thing that still breaks down to work with 100 year old pipes. My few tips:
Bacon grease and cooking oils- pour then into old chinese take out containers and discard in the trash. Wipe out frying pans before loading into dishwashers.
Old towels and bath mats. Notorius for shredding in a washing machine and those fibers are more than likely a poly mix meaning they won't break down but catch on anything you can't get to.
As everyone else has found out: Don't buy toilet wipes and expect them to be flushable. Use a lined trash can especially for them.
If you are a Do It Yourselfer: Your outside cleanout is valuable. While it's running good, make a 2"X2" square "dipstick". Mark the direction of the street lateral and average depth (paint or electric tape) Go one step further and fashion a "clothes pin" tip at the bottom to accept a sewer jetter such as a (clog hog). These are available through many web sites. Works with any pressure washer you have. Having the direction and depth will let you find the path of your lateral and once in, you can jerk the "dipstick" away and let the jetter do its work.
If you have trees nearby, then you may have to resort to a professional as stressed by many before me.

Pathmaker Plumbing


Getting a licensed plumber to do a video inspection BEFORE buying a home is a very valuable piece of advise. As a licensed plumber in the Charlotte, NC area, I have done several of these inspections and have brought to light issues that neither party was aware of. In other cases my inspection revealed the source of some drain problems the seller had but could not understand. The last thing any home owner wants or needs, especially if you're a first time home buyer is a broken sewer repair and associated costs. The same is true for septic tank lines.

A video inspection can answer a lot of questions. It can determine if there is a break (or multiple breaks) in the pipe. If the pipe is disjointed (coming apart underground) or if there is a "belly" or "dip" in the pipe. Often times as tree root systems grow they can push down on a horizontal section of pipe without breaking it, causing the pipe to "belly". This section of pipe, although not technically broken, can create a dam, trapping heavy waste solids and obstructing the flow of water for the whole pipe.
Getting a video inspection can easily illuminate all these problems, and is well worth the cost of whatever a skilled, licensed plumber charges.

Dennie Conley



I know nothing about how anything works in the house, specially not plumbing.

This answered my question at my level of ignorance.

It was clear ,concise and the diagram of sewer main lines thru out the house wasjust what i needed.

It was relatable. I understood it.

I'm coming to ANgies List 1st with these kinds of questions from now on.

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