It may require some trial and error adjusting the dial on the flapper and observing the results over a few days.
Strategy 1. Adjust the dial so the maximum amount of water is left behind in the tank when the flapper closes but the toilet still flushes reliably.
Strategy 2. Put some food coloring in the bowl. Adjust the dial so the coloring is consistently eliminated during the flush.
When cleaning anything including baby diapers, it is better to sweep off or scrape off as much solid and semisolid material as you can first. (1) Less cleaning fluid or detergent needs to be used, (2) Less of a mushy mess which in turn means that bleaches or disinfectants will be more effective.