I just got done reading older posts about this exact issue......single flush toilet 1.6 gal. worked just like any other toilet up until a few months ago..push lever down and let it go......and it flushed completely......now we have to hold handle down a few seconds longer in order for bowl to empty and everything goes down.....it has the canister, which drops down too quickly..i have adjusted the chain, no slack....we havent done anything to mess with it.....it just started up doing it.....as for the folks cleaning under the rim or cleaning out the hole in bottom of bowl etc, acid and all.....i dont see how that stops the canister from dropping too fast........having to flush 2x isnt saving any money.....the waterline in the tank is where water always fills to...nothing changed...it doesnt leak or make noises.....it just stopped flushing fully with the push of a lever......it sucks when you have friends over and have to tell them you got to hold down handle when you flush.......NO, shouldnt have to do that.....any suggestions? oh i tried looking for the model #, and its nowhere.. not on lid or in tank...got it at lowes maybe less then 5yrs ago.. its the elongated one and its the chair height and 1.6 gal...lever on the left side of tank....i keep my bathroom clean..the toilet is cleaned with pine sol....i scrub all under the rim and and bowl....