SINCE THE OLD TOILET FLUSHED, LETS ELIMINATE ANY DRAIN PROBLEMS. THIS IS PROBABLY A 1.6 GAL TOILET. MAKE SURE THE BOWL FILLS COMPLETELY (WATCH THE LEVEL-IT WONT RISE WHEN THE BOWL IS FULL. MAKE SURE THE TANK IS FULL. MAKE SURE THE FLAPPER STAYS UP. STILL WONT FLUSH? PULL THE TOILET TO SEE IF THE WAX SEAL GOT OFF CENTER OFF THE FLANGE OR RUN A CLOSET AUGER THROUGH IT IF YOU HAVE ONE. THE LAST RESORT WOULD BE THE TRAPWAY ON THE TOILET. ALL TOILETS HAVE TRAPS BUILT IN ABOVE THE FLOOR, JUST LIKE UNDER YOUR SINKS (SOME PEOPLE CALL THEM GOOSENECKS). I,VE INSTALLED MORE THAN SEVERAL NEW TOILETS WHERE THE TRAP WAS CLOGGED AT THE FACTORY WITH PORCELAIN, AND BRIGGS IS NO WHERE NEAR MY FAVORITE. RECOMMEND A GERBER OR TOTO.