Normally, when it works properly with the addition of a cup or bucket of water, it is because there is a defect in the jet opening. If this bowl was purchased at a Home Depot or similar store, you probably have a defective unit and need to replace it.: water is bowl does not go down when the tank empties. all new plumbing underneath the floor and drains not plugged. if a large cup of water is poured into the toilet after flushing begins the the ater will flow out and the toilet makes the sucking noise. : the gbowl itself is fairly new. could there be a plugged vent pipe or something preventing : enough air to get to the toilet. trying to sell home a VA inspector thinks toilet is plugged