If the canister flush valve or flapper in a toilet does not lift high enough, it will drop down too soon and provide an inadequate amount of water, causing a poor toilet flush.
To correct this issue, adjust the chain that is attached to the flapper or canister flush valve. The chain should not be loose; allow for only one or two lengths of slack in the chain. Doing so ensures the flapper or canister valve seals properly and provides the correct amount of chain length for a proper flush.
Updated: 7/30/2019