I am in the process of replacing a Fluid Master Flapper valve with a Fluid Master dual flush. My cistern has a 2" outlet, whereas the dual flush has 1 1/2" fittings! Although it says on the box that dual flush would work with 1 1/2" or a 2" outlet, I am not so sure whether the fittings supplied (1 1/2") are sufficient to prevent leaks in the future. Do I need a 2" to 1 1/2" adaptor? Any advise on this would be greatly appreciated.