Quick Answer:
If an upstairs sink or shower drains slowly while the downstairs fixture flows normally, start by checking the upstairs trap and visible drain for hair or debris, run water in both fixtures to compare behavior, and try a hand auger from the upstairs access. If you can’t reach the blockage or the vent looks blocked from the roof, call a professional for camera inspection or safe roof access.
Why This Happens
Partial clogs that only affect an upstairs fixture usually sit in the fixture’s trap or the short branch line that serves that bathroom. Hair, soap scum, and small solids collect near the fixture and reduce flow before they cause a full backup. A blocked vent can also slow drainage by reducing air flow through the system. If the problem is limited to a different level or appears when multiple fixtures run, see Partial clog only in basement and Partial clog when multiple fixtures used for related situations.
Step-by-Step What to Do
1. Remove visible debris and clean the trap
Start at the fixture. Remove the drain cover and clear out hair or gunk you can reach. If the trap under the sink is accessible, place a bucket, loosen the trap slip nuts, and empty it. Clean the trap well and reassemble.
2. Run water to compare upstairs and downstairs flow
With the upstairs fixture running, also run the downstairs fixture and watch the upstairs flow. If running downstairs water changes the upstairs speed, the branch or shared line may be involved. If the upstairs speed does not change, the clog is likely local to the upstairs branch or trap.
3. Try a hand auger from the fixture or access panel
If the trap and visible pipe clean out don’t fix it, use a small hand auger (plumbing snake) through the fixture or an access panel. Feed it slowly, rotate as you push, then withdraw slowly while turning to bring debris out. Repeat until water drains freely.
4. Check the vent stack if possible
A blocked vent on the roof can restrict air and slow upstairs drainage. If you have safe roof access and experience, visually inspect the vent opening for nests or debris. If you aren’t comfortable on the roof, skip this step and call a pro.
5. Call a pro for camera work or difficult access
If snaking from the fixture doesn’t clear the branch or you can’t reach the vent safely, hire a plumber who can run a drain camera or safely access the roof vent. A camera will show whether the obstruction is in the branch, the stack, or further down the line.
What Not to Do
- Avoid disassembling upstairs stacks or removing support elements unless you have the right tools and know how to restore support—this can create leaks or collapse a line.
- Do not attempt roof vent work if you lack safe roof access, fall protection, or experience. Falls are a common source of injury.
- If the clog is in the branch and you cannot access or clear it from safe entry points, call a professional rather than forcing risky access or using extreme measures.
When to Call a Professional
- The obstruction won’t clear with trap cleaning and a hand auger.
- Water backs up into other fixtures, or you see multiple slow fixtures at once.
- You need a camera inspection to locate the clog or the vent requires safe roof access.
- There are signs of pipe damage, repeated clogs, or strong sewer odors.
Safety Notes
- Wear gloves and eye protection when working on drains. Use a bucket under traps to catch water.
- Use a hand auger sized for the fixture branch—don’t force large machines into small access points.
- Never climb onto a roof without proper ladder setup and fall protection; if unsure, hire a professional.
- Avoid mixing chemical drain cleaners with mechanical methods; follow labels and be cautious—they can damage pipes and are hazardous to handle.
Common Homeowner Questions
- Why does only the upstairs fixture slow down?
Because the clog is often local to that fixture’s trap or branch line, or its vent is partially blocked. - Will pouring chemical drain cleaner fix it?
Not reliably for hair and soap scum in a trap; mechanical cleaning is usually more effective and safer for pipes. - How urgent is a camera inspection?
Get one if you can’t clear the clog from the fixture or if the smell, backups, or multiple fixture issues suggest a deeper problem.
More in this topic
For more related fixes and similar symptoms, see Main Line Partial Clogs.