New toilet fill valves often have a clip that attaches to the top of the overflow tube and points the water flow down into the tube without actually having the tube enter the tube. Pretty slick? It works too! Use the clip! 9. Sluggish Flush The toilet could have a partial clog or the actual clog could be downstream from the toilet.
My guess is you have a 1.6 gallon flush toilet and he installed a flapper meant for an older 3+ gallon flush toilet. If this is the case, and I bet it is, you need the correct flapper. My preference so far are the adjustable Fluidmaster ones as it lets me tweak the flush so it slams shut just as the water leaves the bowl.