Quick Answer:
If your bathroom sink keeps running slow and a greasy or filmy layer seems to build up, start by removing the stopper and clearing visible debris, then clean inside the drain and the P-trap. If the thin film returns within days despite basic cleaning, follow the steps below to confirm what’s happening and whether you need professional help.
Why This Happens
When soap mixes with minerals in water, oils from body wash, shaving cream or lotion, and hair, it can form a sticky residue that sticks to pipe walls. Over time that residue narrows the flow and traps more debris. Hard water speeds the process by adding mineral scale that soap binds to. Partial blockages, poor slope, or restricted venting can make the problem show up repeatedly instead of clearing on its own.
Step-by-Step What to Do
Step 1 — Remove the stopper and inspect
- Take out the sink stopper (or lift-out strainer) and clear any hair and loose gunk. Use gloves.
- Look down with a flashlight to see whether you can spot a greasy film higher on the drain walls.
Step 2 — Scrape the drain walls
- Use a flexible plastic scraper, an old toothbrush, or a narrow tool (non-metal to avoid scratching) to scrape inside the drain as far as you can reach.
- Scrape drain walls and observe if film reforms within days. This check tells you whether residue is building in place rather than coming from a single trapped item.
Step 3 — Flush with hot water carefully
- Run the hottest tap water you have for several minutes to soften and wash away greasy soap film. If you have a kettle, pour hot (not boiling) water in stages—avoid pouring boiling water into plastic or older pipes.
- If hot water alone helps, repeat daily for a few days while you monitor the drain.
Step 4 — Use a mechanical tool
- Try a plunger first (cover overflow or adjacent openings) and then a small drain snake or a “zip-it” style tool to pull out film and hair lodged below the stopper area.
- A hand auger can reach deeper; if you use one, feed it gently and pull material out rather than forcing it further in.
Step 5 — Clean the P-trap
- Place a bucket under the trap, loosen the slip nuts, and remove the U-shaped trap. Empty and scrape it clean, then check the trap inlet for buildup.
- Reassemble carefully and test. If the trap is clean but the film reappears higher in the line, the residue is further into the pipe.
Step 6 — Monitor and document
- Note how quickly any film reforms after cleaning and whether it follows certain routines (after shaving, after using a particular product, etc.).
- If cleaning removes the film but it returns in a few days, collect those observations to share with a plumber if needed.
What Not to Do
- Do not add more soap to test drainage.
- Don’t mix chemical drain cleaners with other chemicals or use them repeatedly—those products can damage pipes and are often ineffective on greasy soap film.
- Avoid forcing metal tools down the drain where they can scratch or damage the pipe lining.
When to Call a Professional
Call a plumber if you see any of these:
- The film reforms within days despite thorough cleaning and P-trap removal.
- Water backs up, you get frequent slowdowns in multiple fixtures, or you notice gurgling or sewer smells.
- There are signs of leaks or corrosion when you inspect under the sink, or you’re not comfortable disassembling the trap yourself.
A pro can inspect deeper drain lines, check pipe slope and venting, and advise whether a line cleaning or changes to bathroom products or water softening are needed. If the issue began or worsened after recent work on plumbing, consider checking related troubleshooting like Hair clog after plumbing repair.
Safety Notes
- Wear gloves and eye protection when handling debris or using tools.
- Be cautious with hot water—do not pour boiling water into plastic fittings or directly into a sink with fragile components.
- If you use any chemical cleaner, follow the label, ventilate the area, and never mix different chemicals.
- When in doubt about removing pipes or using a power auger, stop and call a professional to avoid causing damage.
Common Homeowner Questions
- Why does the film come back so quickly? Answer: Repeated formation usually means ongoing residue from daily products or hard water minerals binding with soap in the line.
- Could hair be the main cause? Answer: Yes—hair catches soap residue and speeds buildup; if the problem follows haircuts or shaving, hair is likely involved. See related situations like Bathroom sink clogs after every haircut.
- Will a water softener help? Answer: Often yes—softening hard water reduces mineral soap scum, but it won’t remove existing buildup; combine softening with pipe cleaning for best results.