a white porcelain toilet tank with a black textured wall in the background

Toilet Tank

Originally contributed by Jeff Butler • last updated 12/17/2020

When talking about toilets, there are really only a few things that can go wrong and, unless it's a clogged drain or a leaky toilet seal gasket, most of them will be in the toilet tank. Be careful not to drop the toilet tank cover, it’s heavy.


The tank on a toilet, also called a flush tank or a cistern, is designed to hold a set amount of water that is used to refill the toilet bowl after it has been flushed. Toilet tanks are commonly found directly above and behind the bowl at the back of the toilet fixture. Toilet tanks also contain incorporated mechanisms to release the water from the tank and to allow it to be refilled.

How To Access The Tank And What’s Inside

Typically, on most common toilets, the tank is accessible by lifting the toilet tank cover off the top of the tank basin. Depending on the type of toilet, there are a few possible types of flushing systems contained within the tank:

  • Most commonly, located near the top of the tank or off to the side, there is a fill valve that is attached to either a side-float (also called a ballcock) or a concentric-float. Both the side-float and the concentric-float rise as water fills the tank to a predetermined level and close the fill valve, stopping water from entering the tank.
  • Additionally, attached to the backside of the toilet handle by a chain or lift wire, there is a rubber (sometimes plastic) flapper or ball flush valve mechanism connected to the bottom of the tank. The flush valve covers the outlet (hole) and is held in place against a flush valve seat by water pressure.