Hi all fitting new radiators and need to connect to 8mm micro bore copper pipe under floorboards, (full rework of pipes not an option) would 15mm plastic pipe be okay or just go up to 10mm plastic pipe ? Also best way to connect , compression or push fit ? Using inserts off course , additionally if I drained system down through current radiator valves would there still be a lot of residual water ,combi boiler system ? ( thinking in advance if compression fittings being used as I’m upstairs maisonette and don’t want water running to neighbour )thanks in advance