A toilet leaking from the bottom of the tank is concerning. If the drips are erratic and minuscule in volume, then it may not be alarming but it would still pose a danger to your property. If the leak is substantial, then you should take emergency measures. First, you should find out the actual causes of a toilet leaking from the bottom of the tank.
Check the Components
A toilet may leak if the locknut is loose or not optimally tight. There is a rubber washer in tanks which has a flashing. There could be issues with the flashing or the rubber washer. The surface inside the tank may have cracks or chips, which may compromise the sealing. Here is what you should do.
Get a pipe wrench and attend to the locknut. Just turn it a little and see if it can be tightened further. Don’t exert too much force. That could damage the threads. If the leak is caused due to a loose locknut, then the leak will be contained as you tighten it. Wait for some time to see if the leak persists. Don’t spend a few minutes. Tighten the locknut, wipe the floor and keep it dry, let it be for an hour or longer and then check if there is any water or dampness.
You should look for flashing problems, improper fitting and any kind of damage on the flush valve. The threads could be worn off, the valve may malfunction, there may be excessive rubber in the flashing and the components may not work in tandem. It is possible that the flashing is not working effectively with the flush valve and also the tank. Porcelain tanks often develop chips. Accumulation of debris at the bottom will also need to be looked at. Clean the tank, get rid of debris, uninstall the components, clean them and install them properly. You can use a new silicone sealant or replace the rubber washer if the sealing is wrong or if the present washer has gone kaput.
A toilet leaking from the bottom of the tank could be a circumstantial or situational problem. The leak may not persist all day but you would have water leaking when you flush the tank. In such cases, the problem is in the gasket. The bowl and the tank must touch at the ridge, the wing nuts should be tightened, the sponge rubber gasket should function properly and if you have damaged parts then they must be replaced.