One of our toilets is not visablly clogged (I used the plumbers helper several times and nothing seems to be clogged) however, when I flush the toilet, all the water does not leave the bowl upon that flush. Instead, the bowl fills up about three quarters full but does not leave or release from the bowl - the new water just stays in the bowl. After some time the water level goes back to normal and then when I flush again - the water once again adds to the bowl but does not flush out. Does anyone have any ideas. Thank you - Steven