I need some help diagnosing my toilet trouble. I recently replaced my flapper and was adjusting the tank level. Now my toilet only flushes every other time. when I flush it just fills the bowl up but nothing goes down. The next time I flush everything goes down normal. I have tried adjusting the tank level and the length of time of the flapper being open, but that doesnt seem to work. Do I have a partial blockage in the venting or drain, or something else? Thanks for the help.