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Thanks again Gasman. I think my idiot flat mate has blocked it with wet wipes. The bowl does drain slowly after several hours, but fills again with each flush. I mentioned the flow of water through the sinks and showers because our landlord told us that all water leaving the flat passes through the macerator, which led to believe that the unit itself is still working ok. How much do you think the repair will cost? (I assume it's a job only for professionals?)