If only one drain is slow, you almost certainly have a clog in that fixture's own drain line. If several drains slow down at once, the trouble is probably in the main line they all feed. A five-minute check will tell you which one you have before you pick up the phone.
Why is only one drain slow?
Every sink, tub, and shower has its own short drain pipe, called a branch line. Those branch lines join a bigger pipe, the main line, which carries everything out of the house. When just one fixture is slow, the clog is most likely in its own branch line, close to the fixture.
In a kitchen, grease and food scraps are the usual cause. In a bathroom, it's hair and soap. They build up along the pipe wall until the water has only a narrow path to squeeze through.
What can you try yourself on a single slow drain?
Start with a plunger. Run enough water to cover the plunger cup, seat it flat over the drain, and push and pull with steady, firm strokes. On a double kitchen sink, plug the other drain with a wet rag first so the pressure goes where you want it.
If that doesn't work, a small hand auger from the hardware store can reach a clog in a bathroom sink or tub. Feed it in slowly, and turn the handle when you feel resistance. Stop if it won't move. Forcing it can scratch a fixture or push the clog deeper.
If a plunger and a light auger do nothing, the clog is farther down than a home tool can reach. That's when a licensed plumber and a professional drain cleaning make sense.
Several slow drains at once? Check the main line
The main line is the one big pipe that every branch line empties into. When it's partly blocked, every fixture upstream of the blockage slows down together. The signs to look for:
- The kitchen sink, bathroom sink, and shower are all slow at the same time.
- Gurgling from a drain or toilet when you run a different fixture.
- Water bubbling up in the tub or shower when the washing machine drains.
- A toilet that flushes weakly and keeps clogging, even with a good plunger.
Water follows gravity to the lowest opening in the house. The tub or shower closest to floor level is often the first place a backup shows.
How do you run the five-minute check?
First, run the kitchen sink and the bathroom sink for a minute each and note which one drains slower. Second, flush a toilet and watch the tub or shower drain while it empties. Bubbling or a rising water line points to a shared blockage.
Third, find your cleanout, a capped pipe set in the ground or against an outside wall, often near the house. Don't open it. Water or sewage around it means the line is backed up, and that's a call for a plumber.
If you can't tell which case you have, treat it as the main line. Stop running water in the house until you know more, because every load of laundry and every shower sends more water into a line that can't take it.
Do store-bought drain cleaners help?
It depends on the product and the clog, and the honest answer is that results vary. What doesn't vary is the label. Read it. Drain cleaner labels carry warnings about skin and eye contact, fumes, and mixing one product with another.
If you pour one in and the drain stays slow, you now have a drain full of chemicals. Don't plunge it, and don't pour a second product on top. Tell the plumber what you used and when, so they can protect themselves before they open the trap or run a cable.
What will a plumber do about a main line clog?
A plumber will usually start by finding where the blockage sits. That may mean running a cable, the same tool as a drain snake but longer, through the cleanout. If the clog keeps coming back, a camera inspection shows what's inside the pipe: roots, a crack, a sag that holds water, or a build-up of grease.
Once the cause is known, the fix follows it. A clog of grease or debris may call for hydro jetting or snaking, depending on what the pipe can take. Roots or a damaged section mean a bigger repair, and the plumber should tell you that before any work starts.
Why does the same drain keep slowing down?
A drain that clears and then slows again within weeks has a cause nobody has found yet. Sometimes the cause is habit: grease poured down a kitchen sink, or hair going down a shower with no strainer. A cheap mesh strainer over a tub or shower drain catches hair before it becomes a mat inside the pipe.
Other times the pipe itself is the problem. A pipe that has sagged, cracked, or been invaded by roots will catch debris at the same spot again and again. No amount of plunging fixes that. Clearing the clog treats the symptom. The camera finds the cause.
When should you call a licensed plumber?
Call if more than one drain is slow, if a plunger and a light auger do nothing, if the same drain slows down again after you clear it, or if you see water or smell sewage near a cleanout. Don't wait on a backup that's coming up through a tub or shower. Stop using water in the house and call.
A plumber will ask which fixtures are slow and how long it's been going on, so bring what you learned from the check above. You'll see the price and approve it before any work starts.
If your check points to the main line, or a slow drain just won't clear, ask us about drain cleaning and have a licensed plumber find the cause.
Common Questions
Every fixture has its own short drain pipe, called a branch line. When only one fixture is slow, the clog is most likely in that branch line, close to the sink, tub, or shower.
Results vary, so follow the warnings on the label about skin, eyes, fumes, and mixing products. A plunger is the safer first try, and if you already poured a cleaner in, tell the plumber before they open the drain.
When the kitchen sink, bathroom sink, and shower slow down together, the blockage is probably in the main line they all share. Gurgling, or water bubbling up in a tub when the washer drains, points the same way.
A small hand auger can reach a clog in a single bathroom sink or tub. If more than one drain is slow, or the auger will not move, stop and call a licensed plumber.
