i am trying to fit a basin mate but am having a bit of trouble tightening the waste outlet. the plug hole spins a bit, i cannot get it 100% tight. i have inserted the polystyrene type washer on the inside and the thick washer and plastic nut on the underside, followed by a normal back nut (which came with the waste outlet). i have not used to silicone or mait as advised. but i cannot tighten it, i am using waterpumps. any tips how to get it tight enough?