I have recently installed a new bathroom suite. Its all good except that I can't seem to get a good seal bewteen the cistern and the pan. The doughnut washer is new and I've had the cistern off several times and repositioned it. Everytime when I flush, water must get past the doughnut and then slowly drips through the bolt holes for cistern to pan fixings. Any tips that anyone can offer on getting a watertight seal would be very much appreciated.