Having a slight problem with the basin slow emptying. Plunnging it helps a little, i have taken the trap off and its clear, the pop up waste is clear, the waste runs into the internal soil stack, i think the issue is a flat run of the waste for about 2 meteres along the floor. I did ask the plumber who fitted the en suite to check the waste and renew it if needed, he assured me it was all ok. I have asked him to check it out but he doesnt seem to be interested, i looked at renewing the waste bit its not easy as its well boxed in. I have never used any of the chemical drain cleaners, are these ok to use, is there a trade version which is better than shop bought ones. Any Advice appreciated..Thanks