Why Your Drains Keep Clogging

Why do my drains keep clogging after they are cleared?

The clog was cleared, but the cause was not. A small cable or a plunger opens a channel through the blockage. The ring of grease, soap or scale stays on the pipe wall and catches the next thing that passes.

Repeat clogs on one fixture usually have one of four causes:

• A trap or branch line that has never been fully cleaned
• A habit, such as grease in the sink or wipes in the toilet
• Pipe with a rough or corroded inside wall
• A vent problem, or a line with too little slope

One drain or all of them?

Count the affected fixtures first. This single check tells you more than anything else, and it costs nothing:

What you notice	Likely location	What to do next
One sink is slow	Trap or short branch	Clean the trap, then the branch
Both bathroom fixtures are slow	Shared branch line	Have the branch cleared
Tub gurgles when the toilet flushes	Main line or venting	Call, and limit water use
Kitchen only, repeatedly	Grease in the kitchen line	Clean the full run
Every drain slows after rain	Main line or public sewer	Get it inspected, or report it
Sewage smell near a floor drain	Main line or a dry trap	Check right away

If several fixtures back up at once, read our guide to sewage backing up into the house before you run more water.

What is actually blocking the pipe?

Each room has its own usual suspect.

Bathroom sinks and tubs collect hair and soap film. The trap is a low point, so Wikipedia's plumbing trap entry notes it catches hair, sand, food waste and other debris.

Kitchen lines collect grease. Cooking fat poured down the drain with hot water congeals in cooler pipe. In public sewers, grease causes about half of blockage-related overflows in the U.S., according to Wikipedia's entry on sanitary sewer overflows.

Toilets and main lines collect paper and wipes. So-called flushable wipes do not break down the way toilet paper does, and they snag on rough spots in the pipe. Grease then binds them together.

Older lines add their own trouble. Cast iron can roughen on the inside as it ages, and roots can enter older sewer joints.

What does the clog itself tell you?

What comes out of the pipe is the best clue you will get. Ask to see whatever the trap or cable brings back:

What comes out	What it points to	What to change
Hair and soap film	Normal bath buildup	A strainer, plus a full branch cleaning
White or gray waxy grease	Cooled kitchen fat	Clean the full run, and scrape pans first
Wipes or wads of paper	Flushed products, or a rough spot in the pipe	Bin the wipes, then camera the line if paper still catches
Fine roots	An open joint	Camera first, then a repair
Rust flakes or black scale	Aging cast iron	Camera before any hard cleaning
Sand or grit	A break letting soil in	Camera soon

Are flushable wipes really safe to flush?

No, treat every wipe as trash. Wipes do not break down when flushed, and they catch on rough spots in a pipe, as Wikipedia's fatberg entry explains. Grease then binds them into a solid mass, the same process behind the huge blockages that make the news.

A house line has less room for error than a public main. One wipe may pass. A habit of them, in an older pipe with a rough wall or a slight sag, gives every later flush something to catch on. Keep a small bin beside the toilet and the problem goes away for free.

The flushable label has drawn regulators too. In 2015, the FTC alleged that one maker of flushable moist tissue lacked adequate support for its claims that the product was safe for sewer and septic systems, because its testing did not reflect real-world conditions after flushing.

Could the line under your slab have sagged?

Yes, and it is a common reason for a repeat clog that nothing seems to fix. Houston sits on clay soil, which swells when wet and shrinks when dry. When the ground moves, a buried drain can lose its slope or form a low spot, called a belly, where solids settle.

Cleaning a belly helps for a while, and then it fills again. A sewer camera inspection shows the problem, since the camera will pass through standing water at the low point.

Could a blocked vent be the real problem?

Yes, and no cable will find it. Every drain needs air behind the water, and that air comes through a vent pipe that runs up through the roof. If leaves, a nest or a dropped object block it, water drains in gulps and pulls air through the nearest trap. You hear that as a gurgle. It can also pull a trap dry, and sewer smell follows.

Watch for a sink that glugs after the tub drains, a toilet bowl that dips when another fixture runs, or slow drains with a clean camera run. Remodels can cause the same trouble when an island sink or a moved vanity goes in without proper venting.

What our team would try before booking a visit

Start with the simple, cheap fixes. Our team's general advice for a single slow drain:

1. Pull the stopper and remove any hair by hand.
2. Plunge with the overflow covered, using a cup plunger for sinks.
3. Put a bucket under the trap, remove it and clean it, if the fittings are plastic and in good shape.
4. Use a small hand auger for the next few feet.
5. Run water and check for leaks at the joints.

Skip the chemical drain openers. They are harsh on skin and eyes, they often leave a pool of caustic water behind, and they make the next repair riskier for whoever opens the line. Tell a plumber if you have already used one.

When is it time for a plumber?

Call when simple steps fail, or when more than one drain is involved. A drain cleaning visit clears the line properly, and the method should match what is in it.

A cable is fine for a local clog. Hydro jetting uses high-pressure water to scour grease and scale from the pipe wall, which is why it suits repeat clogs. A camera comes first if the pipe might be cracked, because jetting a broken line can make it worse.

Bring a clog log if you can. Write down the date, the fixture and what had just run. Clogs on a steady cycle point to buildup, clogs after rain point to the main line or the public sewer, and clogs after laundry point to a line that cannot carry a large volume.

Stopping the next clog

Most repeat clogs end when the buildup is gone and the habit changes:

• Use a hair strainer in every tub and shower.
• Wipe pans before washing them.
• Put wipes in the trash, whatever the package says.
• Run the disposal with plenty of cold water, and go easy on fibrous scraps.
• Note how often a drain slows, and tell the plumber.

Homes in Pasadena and the rest of the Houston area face the same mix of clay soil, grease and aging pipe. When a drain keeps coming back, stop treating the symptom and find out what is underneath it.