What Causes Clogged Drains? Here Are the Most Common Culprits

Clogged drains are one of the most common plumbing problems for Seattle homeowners — but the causes aren’t always as obvious as they seem. From everyday hygiene products to tree roots in pipes deep underground, there are many ways buildup can sneak into your plumbing system over time.

At Bob Oates Plumbing, Sewer & Rooter, we’ve spent more than 30 years solving drain issues throughout the Greater Seattle Area. Here’s a clear look at what causes clogs, how to prevent them, and when it’s time to call in the pros.

1. Hair — The Most Frequent Bathroom Offender

Hair is responsible for a large percentage of bathroom drain clogs. When combined with soap residue, shampoo, and oils, it forms tough, rope-like tangles inside the pipes.

Over time, these clumps trap more debris and restrict water flow. A simple mesh drain screen can prevent most hair from entering the drain in the first place.

2. Soap Scum and “Fancy” Body Products

Most soaps contain fats or oils that leave behind a filmy residue called soap scum. Moisturizing body washes, conditioners, and oil-based skincare products add to the problem by coating the inside of your pipes.

As this residue hardens, it becomes a sticky surface that catches hair, dirt, and other debris — eventually forming a blockage.

Tip: Running hot water for 20–30 seconds after a shower helps reduce buildup.

3. Grease and Oil Buildup

Even small amounts of grease from washing hands, shaving, or rinsing skincare products can accumulate in bathroom sinks. As the grease cools, it solidifies and traps other particles, narrowing the drain line.

Grease-related buildup is even more common in kitchen drains — and pouring it into the sink is one of our four things you should never do to pipes — but it can happen anywhere water meets oil.

4. Foreign Objects

Many clogs start by accident. Items like:

• Dental floss

• Cotton swabs

• Bandages

• Makeup wipes

• Toys (kids!)

• Hair ties or clips

…can easily get stuck in the drain or toilet trap. Even “flushable” wipes are notorious for causing slow drains and full sewer blockages.

5. Store-Bought Chemical Drain Cleaners

This one surprises people: over-the-counter chemical drain cleaners often cause more harm than good.

These products:

• Generate extreme heat

• Warp PVC pipes

• Corrode older metal pipes

• Push clogs deeper into the sewer line

While they may provide temporary relief, chemical cleaners weaken plumbing over time and can turn a small clog into a major repair.

Learn more: 4 Hidden Dangers of DIY Drain Cleaner Chemicals — and What Actually Works 

6. Tree Roots in Sewer Lines

Outside the home, tree root invasion is one of the biggest threats to your sewer system. Seattle’s mature trees seek moisture, and tiny cracks in older sewer pipes become the perfect entry point.

Once inside, roots expand, catch debris, and eventually block the entire line. Signs include gurgling drains, recurring backups, or slow drainage throughout multiple fixtures.

Only a professional sewer inspection or hydro jetting service can fully diagnose and clear tree root intrusion.

Preventing Clogged Drains — Simple Steps That Protect Your Home

A few proactive habits can dramatically reduce clogs:

• Install mesh screens in showers and tubs

• Avoid flushing wipes or hygiene items

• Run hot water after showers

• Schedule routine drain cleaning (especially in older homes)

Annual maintenance is especially helpful in Seattle homes with aging plumbing or history of sewer issues.

When to Call a Professional

If you’re dealing with:

• Recurring clogs

• Slow drains throughout the home

• Gurgling noises

• Foul sewer odors

• Backups in tubs or sinks

…it’s time to bring in a professional drain cleaning technician. A camera inspection can pinpoint the cause and prevent bigger issues down the road.

At Bob Oates Plumbing, Sewer & Rooter, we offer fast, reliable drain cleaning services, hydro jetting, and sewer inspections to keep your home running smoothly.

Need help with a clogged drain? Call us or schedule service online — we’re always here to help!