Illustrative image of the relevant drainage feature or investigation.
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Get quotes from local drainage specialists ↗What to look for first
Hair and soap residue collect around a shower trap before the underground drainage is involved. Compare shower drainage with the washbasin and toilet in the same bathroom.
Before arranging disruptive work, separate what has been observed from what is only suspected. Ask whether one outlet is involved or whether several drain to the same point.
What else might cause it?
A slow shower alone rarely proves that a main drain has collapsed. Drainage faults can overlap with surface-water problems, poor plumbing connections or unusual weather, so timing and location deserve attention.
Getting the right work done
A plumber can inspect accessible traps; drainage specialists investigate shared external restrictions. Ask for a clear explanation of the problem, the proposed method and what evidence will show that the work was successful.
Before you agree to major work
Get the proposed work and its limits in writing. For costly repairs, ask for photographs or survey evidence locating the defect and consider a second quotation. Where the affected run may be shared or adopted, check ownership before arranging privately funded work.