very cheaply these days: just tie a bottle brush to the end.
Nah, already got a 3m long one of those. I'm reluctant to try taping a bottle brush to the end, as the pipe run has a couple of 45° bends before going into a top entry on the toilet connection elbow, and I have this dread of the brush coming adrift and me having to take a load of panelling apart on the combined vanity unit and toilet backing. 'S gotta be a brush actually twisted into the end of the twisty wire. Found a supplier in the US who'll make 'em to whatever length you want, but the shipping would be prohibitive for something that costs no more than a few pounds.
I recently unblocked a complex small bore drain run by deliberately blocking the outlet end and back filling the whole system with caustic soda solution and left it to soak for several hours.
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