Has anybody used one of these Geberit combined waste/ overflow system? We have two of these and not sure whether to use them or not. The problem is the sink does not have an overflow unless this system is used but I do not really want a pull up lever on the taps. I think you can get a separate rotating knob but have not managed to source one yet. The only other option is not to use this and just put in a pop up waste and hope nobody leaves the tap running. Any ideas of what people have done would be very much appreciated. TIA