Toilet Flange, Toilet Flanges, Toilet leak at base, Leaky Toilet, Toilet Leaking , Install Toilet, Install Toilet Flange ShimThe bottom side of the top lip of the toilet flange should be flush with the finish floor. This is known as the height, which is critical to the toilet sealing properly. When bathroom flooring is replaced the finished floor will often change heights and the toilet flange is neglected. A toilet flange shim shown here can be installed as a permanent solution and is half the price as a toilet flange replacement.