We bought a house recently, and the toilet upstairs is not emptying properly. When I flush it, the water slowly rises up and then returns slowly to it original position never completely emptying the bowl. What could be causing this? Is it an obstruction in the drain? Could it be that the flapper wasn't allowing enough water out of the tank and into the bowl forcing the "old" water out? I have pulled that toilet and will be replacing it. Just wondered if there was anything that should be done before I install the new toilet.