The base of the cistern must be level. If like me you tilted it by screwing it to the wall you will spoil the seal . Coat the new doughnut washer with plumbers seal (from wickes) top and bottom and the top of the pan then tighten the wing nuts evenly.When screwing into the wall make sure the cistern does not tilt. I was surprised that such a small tilt could cause a leak as the water pressure is much less and the washer is so thick.
eddie from leeds
February 2010