A drain stopper installed in a sink should be operated with the down rod handle on the top of the faucet. It will stop the sink from draining when closed. Sometimes the stopper comes loose from the bar inside the sink drain outlet and must be reattached to work properly again. The rod assembly is taken apart under the sink and put back together so that the stopper is again attached to the bar arm that moves it into the closed or open position.
From under the sink, find the down rod assembly coming from the down rod handle on top of the faucet to the stopper bar on the back of the sink outlet. Remove the nut holding the stopper bar in place on the back of this outlet. Place the drain stopper back into the sink with the hole in the bottom of it aligned for the stopper bar to be attached.
Pull the bar out until it can be reinserted back into the hole in the bottom of the drain stopper.
Push the bar back into the outlet, making sure it fits into the hole at the bottom of the stopper. Test that it is in the proper place by moving the bar up and down and verifying the stopper in the sink moves with it.
Tighten the nut that holds the bar into the outlet by hand and give it a quarter turn with the wrench.
Adjust the down rod and stopper bar assembly under the sink if the stopper does not fit tightly.
Failure to tighten the nut holding the bar assembly to the back of the sink outlet could cause water damage.