Toto Drake -- what part is this?

I installed my Drake tank on my round front bowl tonight for the umpteenth time (second tank -- first had constant slow leak from left tank bolt that after five tries we gave up on and traded in at the plumbing supply we got it from) after taking off the flush valve nut, sanding down the tank, and putting it back. (This is the second try with this tank...first try had tiny slow leak coming from center area so I'm hoping that sanding and retightening will solve it. Bolt holes were sanded before the first try, I learned my lesson.) When I hooked everything back up the chain wasn't long enough to allow the pink flush valve to seal up and the tank to fill. Took the chain off and added a link...and discovered this 1.5" long piece of plastic tube at the bottom of the tank. Oops.

Other than my many times removing and putting the tank back on to solve the leak problems, I know zip about the toilet innards -- what is this piece and where do I need to put it back? I think it may have slipped off the chain when we added the link, but maybe not. Hopefully I don't have to empty it and take the tank off again...

Picture attached.

TIA.

That part is on the chain, that is, the chain goes through it.

Thanks Terry, I knew you'd be able to enlighten me. What is its purpose? I'll put it back on tomorrow, as long as the darn thing hasn't started leaking, in which case you will probably find me locked up in an asylum babbling about gaskets and snugging.

Don't mean to sound rude, but how much is that frustration worth to you? $100, $200, or more?

At the moment, a lot. You're welcome to come over and give me a hand (unless you're looking for $200, which I don't have right now) but I suspect it would be a bit of a hike for you.

one more thing...

One more question...when we put the flush valve nut back on and stuck the apparatus back in it, it looks like we put it in at a non-factory angle. Is this going to be a problem in the future? It's such that now the hinge (?) is butting right up against the side of the tank. I'm probably being over-paranoid but I want this to work right. You can't tell in the picture but I did put the plastic tube back on.

Picture below, TIA.