As the title says. I've installed a belfast sink over the weekend and the waste just keeps leaking. Firstly I put plumbers mate under the waste and tightened the plastic lock nut. Water is finding its way under the chrome waste (85mm in diameter) and trickles down the thread. After speaking to a pipe fitter at work I used silicone mastic under the waste, tightened the plastic lock nut under the sink and f""" me it still leaks. I'm running out of patience so good advice needed please