Is a slow drain always a plumbing problem?

Not always. A single slow fixture is often a local clog in the trap or branch line. When several fixtures slow down together, or a lower drain backs up when an upper one runs, the main line is the more likely cause and that is worth a professional look.

Should I use chemical drain cleaner first?

It can damage older pipes and it makes the job harder and less pleasant for whoever opens the line. Mechanical clearing by a plumber is the safer route, especially for repeat clogs.

Service Explainers

Warning signs you need to call a plumber

How to tell the difference between a minor plumbing annoyance, a problem worth booking, and an emergency that should not wait until morning.

By Elijah Canfield, Founder, Hire Best Pros · Updated August 26, 2026

Elijah Canfield is the founder of Hire Best Pros. He writes and edits the site's consumer guides, with a focus on how home service and moving projects are priced, scoped and compared.

A plumber repairing a supply line under a kitchen sink

Call a plumber when water is going somewhere it should not, when drainage slows across more than one fixture, when pressure drops without explanation, or when you smell sewage or gas. Treat anything involving an active leak, a backed up sewer line, or a water heater that is leaking or making banging noises as urgent. Shut off the water at the fixture or the main valve first, then call.

Key points

One slow drain is usually local. Several slow drains point at the main line.
A sudden jump in the water bill with no change in habits often means a hidden leak.
Know where your main shutoff valve is before you need it.

Signs worth booking a visit for

Drains that gurgle, empty slowly, or back up when another fixture runs
Water pressure that has dropped at several taps
Running or rocking toilets, or a toilet that needs a second flush
Damp cabinets, stained ceilings, warm spots on a slab floor, or a musty smell near plumbing walls
A water heater past its expected service life, or one that produces rusty water

Signs to treat as an emergency

Some situations get worse by the hour. Sewage backing up into a tub or floor drain, water spraying from a supply line, a leaking water heater, or the smell of gas near a gas fired appliance all justify shutting off the water or the appliance and calling for help right away.

Sewage odor indoors or waste backing up at the lowest drain
Water leaking from a supply line, valve, or the base of a water heater
No water at all, or water that is discolored across the whole house
Any gas smell near a water heater or boiler, which means leaving and calling the gas utility first

Need a plumber to look at it?

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What you can safely do before the visit

Shut off the fixture valve, or the main valve if the leak is not at a fixture
Clear the area under sinks so the plumber can work
Stop using the affected drain instead of adding chemical drain cleaner
Photograph the damage if you may file an insurance claim

Common questions

Is a slow drain always a plumbing problem?: Not always. A single slow fixture is often a local clog in the trap or branch line. When several fixtures slow down together, or a lower drain backs up when an upper one runs, the main line is the more likely cause and that is worth a professional look.
Should I use chemical drain cleaner first?: It can damage older pipes and it makes the job harder and less pleasant for whoever opens the line. Mechanical clearing by a plumber is the safer route, especially for repeat clogs.