Illustrative photograph; a drainage survey is needed to establish the actual fault.
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Get quotes from local drainage specialists ↗Start with the likely route
A WC pan trap can hold an object, while a shared branch can restrict several appliances. Check whether the shower or basin rises or gurgles when the toilet is flushed.
Where possible, establish whether the trouble starts at a local fitting, a branch pipe or the underground run. This distinction can prevent an unnecessary survey of the whole system.
Don't overlook another explanation
A one-off blockage does not automatically indicate a damaged underground drain. If the visible problem changes after rainfall, flushing or use of a particular appliance, record that sequence so the contractor can test the right part.
Questions to put to the contractor
A drainage contractor can distinguish a pan blockage from a restriction downstream. Ask what will be done first, what the inspection cannot tell you and whether the quotation includes reporting and reinstatement.
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.