On Dec 8, 10:46*am, Me wrote:
This toilet has been dry and out of use for several months and is about
two years old. After reconnecting it with a new seal and the cold water
line tight with no leaks, it leaks like a gushing river whenever flushed.

It's fine sitting with a tank full of water - no leaks at all. But the
minute the toilet is flushed, what a mess of water on the floor.

Which seal/gasket do I need to replace?

Did you scrape up all the old wax and put a new wax ring down before
placing the toilet on the floor?

I have had some luck reusing wax if it's not too old but you still
have to scrape it back into a ring so it can be pressed down again.
Since a wax ring is only a couple bucks it's not worth it unless
you've got no other reason to make a supply run.