Common Causes of Clogged Drains
A slow drain is easy to ignore. Then one day the shower is standing six inches deep and the kitchen sink won't empty at all. Clogs rarely happen all at once, they build up gradually, and by the time you notice them, the blockage is already significant.
Understanding what causes clogs in each area of your home makes prevention straightforward, and knowing the difference between a DIY fix and a professional job saves time and avoids making things worse.
Key Takeaways:
Shower and bathtub clogs are almost always hair and soap scum accumulation near the drain. A hair catcher and monthly maintenance flush prevents most of them.
Kitchen clogs are primarily grease and food debris. Never pour cooking oil or grease down the drain.
Dishwasher drainage problems often start with a clogged filter or a slow kitchen sink drain, not the dishwasher itself.
Multiple slow drains at once signal a main line blockage, which requires professional equipment to clear.
Chemical drain cleaners are a short-term fix that can damage pipes over time. Mechanical clearing is more effective for stubborn or recurring clogs.
Bathroom Drains
Shower Drains
Hair is the primary culprit in shower drains. It combines with soap residue, shampoo buildup, and body oils to form a sticky mass that accumulates just below the drain cover over time. In larger households or homes where anyone has long hair, this can become a significant blockage within weeks without a drain cover in place.
Hard water contributes here too. Phoenix's mineral-heavy water leaves soap scum and calcium deposits on pipe walls, narrowing the drain opening gradually and giving hair and debris more surface area to cling to.
DIY prevention:
Install a drain hair catcher and clean it after every few showers
Run hot water for 30–60 seconds after each shower to flush residue down the line
Pour a half cup of baking soda followed by a half cup of white vinegar down the drain monthly, let it sit 15 minutes, then flush with hot water
When it's already slow: A drain snake or zip-it tool pulled through the drain cover will usually pull out the hair clog directly. If the drain is still slow after clearing visible buildup, the blockage may be further down the line.
Bathtub Drains
Bathtub clogs share the same causes as showers, hair, soap scum, and mineral buildup, but bathtubs have one additional factor: the stopper mechanism. The pop-up or trip-lever stopper assembly sits just below the drain opening and is a common place for hair and debris to accumulate around the linkage. In many cases what looks like a deep clog is actually buildup on the stopper mechanism itself.
DIY fix: Remove the stopper (most unscrew or lift straight out) and clean the linkage and stopper thoroughly before reaching for a snake.
Bathroom Sink Drains
The pop-up drain assembly in bathroom sinks is the most common culprit. Hair, toothpaste, soap, and shaving debris collect around the pivot rod and stopper linkage just below the drain. Most bathroom sink clogs are within the first several inches of pipe and are easily cleared.
DIY fix: Remove the stopper by lifting or unscrewing it and clear the buildup around the pivot rod. A zip-it tool or bent wire hanger can pull debris out if the stopper isn't removable. If clearing the stopper doesn't resolve it, the P-trap under the sink is the next place to check.
Kitchen Drains
Kitchen drain clogs are almost always caused by grease, oil, and food debris, and they tend to sit deeper in the line than bathroom clogs.
Grease and Oil
Cooking grease is the single biggest driver of kitchen drain problems. It goes down the drain as a liquid but cools and solidifies on pipe walls as it moves away from the heat of the sink. Over months and years, that layer builds up and narrows the drain until flow slows significantly or stops. Coffee grounds and food debris then stick to the grease layer, compounding the blockage.
The biggest misconceptions:
Pouring boiling water behind grease temporarily melts it further down the pipe, where it re-solidifies and creates a clog deeper in the line, harder to reach and harder to clear
Dish soap does not dissolve grease in pipe walls the way it does in a hot sink
DIY prevention:
Pour cooled cooking grease and oil into a container and dispose of it in the trash, never the drain
Run cold water when using the garbage disposal, cold water keeps grease solid so it travels through the line rather than coating pipe walls
Wipe greasy pans with a paper towel before rinsing
Food Debris
Even with a garbage disposal, certain foods cause problems in drains:
Fibrous foods (celery, artichokes, asparagus) wrap around disposal blades and accumulate in pipes
Starchy foods (pasta, rice, potato peels) swell with water and form a thick paste in the drain
Coffee grounds don't break down and accumulate rapidly in the trap and beyond
Eggshells create fine granular waste that combines with grease to form a stubborn sludge
DIY fix for kitchen clogs: A plunger with a flat bottom cup (not the flanged toilet plunger) over the drain opening can dislodge a clog in the trap. If plunging doesn't clear it, the P-trap under the sink can be removed and cleaned directly. Do not pour chemical drain cleaners repeatedly into a kitchen drain, they degrade pipe connections over time and rarely fully clear grease-based clogs.
Dishwasher Drains
Dishwasher drain problems are often misdiagnosed. Standing water at the bottom of the dishwasher is almost always a drain issue, but the cause may be in the dishwasher itself, the drain hose, or the kitchen sink drain it connects to.
Common causes:
Clogged dishwasher filter: Most dishwashers have a filter at the bottom of the tub that catches food debris. Many homeowners don't know it exists. A clogged filter restricts drainage and is the first thing to check.
Kinked or blocked drain hose: The drain hose runs from the dishwasher to the sink drain or garbage disposal. A kink, a clog in the hose, or a blocked knockout plug in the disposal inlet can prevent drainage.
Clogged sink drain: The dishwasher drains through the same line as the kitchen sink. If the sink drain is slow, the dishwasher will often drain slowly or back up too.
Air gap: Homes with an air gap fitting on the countertop (the small cylindrical cap near the faucet) can experience drainage problems if the air gap is clogged. Removing the cap and cleaning it out often resolves the issue.
DIY check: Start with the filter (check your owner's manual for location and removal instructions), then inspect the drain hose for kinks, then check whether the kitchen sink drain is slow. In most cases, dishwasher drainage problems are resolved without calling a plumber.
Clogs Deep in the Pipe
Clogs deep in the main drain line are a different problem from fixture-level clogs. They tend to affect multiple drains at once, if your toilet, shower, and sink are all draining slowly or backing up at the same time, the blockage is likely in the main line rather than at any individual fixture.
Main line clogs are most commonly caused by:
Grease accumulation over years of use, particularly in older homes
Tree root intrusion, where roots enter through joints or cracks in the sewer line and grow into a blockage over time
Scale and mineral buildup in older pipes, particularly in galvanized steel systems
Non-flushable items that make it past the toilet trap and into the line
A plunger or a standard household drain snake won't reach a main line clog. These require a longer professional drain auger or, for root intrusion and heavy grease accumulation, hydro-jetting to clear. Hydro-jetting uses high-pressure water to cut through roots and blast grease buildup off pipe walls completely, rather than just punching a hole through the clog the way an auger does. A camera inspection is often the fastest way to confirm the location and cause before deciding on the best approach.
When to Call a Professional
DIY drain cleaning handles most fixture-level clogs effectively. It's time to call a plumber when:
Multiple drains in the home are slow or backing up at the same time
A drain backs up into another fixture (toilet water rises when you run the sink, for example)
You've cleared the obvious obstruction and the drain is still slow
You're dealing with a recurring clog in the same location, which often signals a pipe issue rather than a buildup problem
There's a sewage odor coming from drains
Chemical drain cleaners are worth a mention here. Products like Drano can clear a minor clog in a plastic P-trap, but they contain caustic chemicals that degrade older metal pipes and rubber seals with repeated use. They also don't fully clear grease-based clogs or reach blockages deep in the line. For recurring or stubborn clogs, a mechanical solution, a snake, auger, or hydro-jet, is more effective and less damaging to your plumbing.
Prevention Is Cheaper Than a Service Call
The most effective drain maintenance is consistent and simple: keep grease out of the kitchen drain, use a hair catcher in the shower, and don't flush anything other than waste and toilet paper. Most of the serious clogs we clear in Mesa homes were preventable.
If you're dealing with a slow drain or a clog that isn't clearing on its own, Superstition Plumbing serves Mesa and the East Valley. We've been clearing drains and diagnosing the underlying causes for over 45 years.
