Oops ... be careful with your overflow tube
In trying to remove a faulty water conservation flush valve I stressed the overflow tube ... and broke it off. OOPS. It was cheap and weak anyway. ... Replacement of the overflow tube requires removing the tank from the bowl, installing a new overflow tube and gasket, and reinstalling the tank. Sleeves rolled up, ready to learn....
I didn't have this guide in front of me to help, so I relied upon advice from the hardware store employees. This isn't rocket surgery, just a few bolts and off she comes. ... Don't be shy about asking those workers if they've done this, and what they recommend!
But. Using a cheap seal, I had a slow leak after reassembly that I just couldn't stop no matter how much I doinked around with the tank bolts. Finally took it apart, put in a name brand seal, and it worked a treat. What I didn't plan on was the cheap overflow tube, cheap seal, replacement tank bolts actually cost me more than the name brand kit which contains the overflow tube, seal, and tank bolts. Derp.
Don't buy the cheap parts at the hardware store. Get the name brand parts which will include all or even more than you need.
Buy new hardware for everything. Even if you're tank bolts and gaskets aren't bad, replace them with brand new ones anyway. For one thing, they'll be cleaner. The gaskets will install better than old ones that may break on you. And finally, you'll be proud of your fine repair work with shiny new parts. Go 'head, gaze upon and admire your nice new parts and repair job !