You mean you cannot take the lid off the toilet tank?
Also by overflowing into the basin, do you mean it is draining but the toilet keeps running? Not overflowing onto the floor?
Yes the lid seems to attached to something inside.
It is draining but the toilet keeps running.NOT ONTO THE FLOOR.
Does the toilet flusher the handle that flushes the toilet go through the tank lid? If it does and it isn't on the side of the tank, the chain would be attached to the toilet tank lid.
If the handle is on the side of the tank there shouldn't be anything attaching itself to the lid. Can you lift it a little and see a chain attached to it. The reason the toilet may be running could be a few different things, the flapper might not be sealed completely, The fill valve may not be shutting off all the way or water level set too high and overflowing into the fill tube. My recommendation to solve the problem once you get the lid off will be to replace toilet fill valve, Fluidmaster is my recommendation for a replacement, and perhaps replace the flapper or ball. Both parts can be found at your local hardware store or big home improvement store, Home depot ect.
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