I`ve seen 3" soil working fine @ an old house but it was lead and had vents etc. and done by craftsmen Was repairing a 2 1/2 gallon Cistern on the ancient syphonic WC - so asked about the small pipework ...Never had any bother . They didn`t like paying so maybe they were tight ar sedI think thats why they're not used! College was 20 years ago, legislation could well have changed since... I certainly wouldnt install a pan on a 3" pipe. Bad enough when 4" blocks!!!!
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