Why Your Drain Keeps Clogging, and When It Is the Main Line

A drain that clogs once is an inconvenience. A drain that clogs again a few weeks after you cleared it is a symptom. Plungers and store-bought cables push a hole through the blockage, but they leave the cause in place, and the cause is what brings the clog back. The first job is working out whether the problem is in one fixture’s drain or in the main line that every drain in the house empties into.

One drain or all of them?

This is the question that matters most, and you can usually answer it in a few minutes.

One fixture is slow and everything else is fine. The blockage is in that fixture’s branch line, somewhere between the drain and the point where it joins the rest of the system. Kitchen sinks, bathroom sinks and showers account for most of these.

Several fixtures are slow, or something odd happens when you use one of them. That points to the main drain or the sewer lateral outside. Watch for:

• The lowest drain in the house backing up first, often a basement floor drain, a ground-floor shower or a tub.
• Water rising in the tub or shower when the toilet is flushed.
• Toilets gurgling when the washing machine drains or a sink empties.
• More than one toilet running slow at the same time.
• A sewage smell from floor drains, or water coming out of the cleanout pipe in the yard.

If you see these, stop using water in the house as much as you can. Every flush and every load of laundry has to go somewhere, and with a blocked main that somewhere is your lowest drain. This is the point to call for main drain cleaning rather than reaching for the plunger.

What usually causes a repeat clog

Where the clog is tells you a lot about what it is made of.

Kitchen lines clog with grease. It goes down warm and liquid, cools inside the pipe and coats the walls, catching food scraps as they pass. A cable punches through the middle, but the coating stays, and the pipe narrows again. Scraping pans into the bin before washing does more for a kitchen drain than any cleaner.

Bathroom lines clog with hair bound together by soap scum. A simple hair catcher over the shower drain prevents most of these.

Toilets and main lines clog with things that should not be flushed. Wipes labeled “flushable” are the usual culprit: they pass through the toilet but do not break down the way paper does, and they snag on any rough spot in the pipe below.

Main sewer lines clog for reasons that have nothing to do with what goes down them. Tree roots find their way into the joints of older clay and cast iron pipe and grow into a mat that catches everything. Older cast iron can build up scale on the inside until the pipe is a fraction of its original size. And a section of pipe that has settled into a dip, called a belly, holds standing water and waste that slowly builds into a blockage.

Snaking, jetting and the camera

Plumbers have three main tools for a stubborn drain, and they do different jobs.

Drain snaking feeds a rotating steel cable through the line to break up or pull out the blockage. It is fast and it is the right first step for most single-fixture clogs. Its limit is that it opens a path through the blockage rather than cleaning the pipe wall.

Hydro jetting sends water through the pipe at high pressure through a nozzle that sprays backward and outward, scouring the full inside of the pipe. It removes grease coatings, soft scale and fine roots that a cable leaves behind, which is why it is the usual answer when the same line keeps clogging. It is not suitable for every pipe; a line that is already cracked or badly corroded may need to be inspected first.

A sewer camera inspection puts a waterproof camera down the line so you and the plumber can see what is actually in there: roots at a joint, a belly, a crack, an offset where two sections have shifted apart, or simply a clean pipe with a grease problem. If a main line has clogged more than once, the camera is worth doing before paying for another cleaning, because it tells you whether cleaning can fix it at all.

When cleaning is not enough

Some problems cannot be cleared, only repaired. A collapsed section, a pipe that roots have cracked open, or a belly deep enough to hold waste will keep clogging no matter how often the line is cleaned. The camera footage shows which of these you have, and where.

The repair depends on the damage and on what is above the pipe. A single broken joint can often be dug up and replaced on its own. Longer runs of damaged pipe can sometimes be lined or replaced with trenchless methods, which avoid digging a trench across the yard or driveway. Where the pipe has failed along most of its length, sewer line replacement is the lasting fix.

It is worth knowing who owns what. In many places the homeowner is responsible for the sewer lateral from the house all the way to the public main, including the part under the street, but the dividing line varies by city. Your local sewer utility can tell you where yours sits before you decide on a repair.

A word on chemical drain cleaners

Caustic and acid drain cleaners generate heat as they work. In older metal pipes and in plastic pipe joints, repeated use can do real damage, and a cleaner that does not clear the clog leaves a pool of corrosive liquid sitting in the fixture for whoever opens the drain next. If you have already poured one in, say so when you call, so the plumber knows before they start.

Keeping it clear

Most repeat clogs are preventable:

• Keep grease, coffee grounds and fibrous food scraps out of the kitchen sink.
• Put a hair catcher on every shower and tub drain.
• Flush only toilet paper, whatever the packaging on the wipes says.
• If you have large trees near the sewer line and a history of root clogs, ask about scheduled cleaning before the roots close the pipe again.

If the same drain has clogged more than twice in a year, it is time to stop clearing the symptom and find the cause. A clogged drain repair visit that ends with a camera look at the line usually answers that in one trip.