There are several causes of toilet pipe leaking. You may have a leak in the supply pipe or the waste pipe. Both are discomforting, the latter more so because it is the waste pipe. The supply pipe leaking will only have water while the latter will create an unhygienic condition. Let us list the causes of toilet pipe leaking by highlighting all possible issues you could have in the supply pipe and the waste pipe.
The leak could be due to a loose nut at the supply line. This nut connecting with the fill valve needs to be tightened. It could also be the nut connecting the shut off valve. The valve connected to the water line will have an attachment or the connection itself could be faulty. The valve’s washer could have a problem and that may facilitate the leak. The bottom line is there happens to be a crack, gap or unsealed part somewhere that is allowing water to leak through the supply line.
You should try to tighten all the nuts, check all the valves if they are fine and also reduce the water pressure in the supply line just to ensure that the various components of the toilet are capable of withstanding the thrust. It is possible that a fully loaded tank or when the water comes gushing into the mains, the increased pressure will be unbearable for the valves, nuts and the pipes. If the valves or nuts and the pipes are beyond repair or do not function optimally even when the water pressure is optimum, replace whichever part is damaged.
The other type of toilet pipe leaking is the waste pipe letting some water drip out. This could be the standing water in the bowl or the gush of water when you have flushed the toilet. This is a more concerning scenario since you wouldn’t be confined to a leak but a possible sanitation disaster. This type of leak happens when there is a problem with the seal that connects the waste pipe with the drain pipe. It may also happen if the waste pipe or the drain pipe has some kind of structural damage. The connection is supposed to be seamless, airtight and waterproof.
All wastewater, including heavy flushes, should smoothly flow out the toilet through the waste pipe onto the drain pipe and thereby to the sewers or septic tank. You will have to change the waste pipe and in some cases the toilet itself.