Flush Valve Seal
These are some common tools used to work on this device. You might not need every tool for every procedure.
Permanent Fix for Loose Toilet Seat ¶
The problem with toilet seat hardware is that the holes in the china bowl are a bit oversize for the two bolts that secure the seat, allowing the seat to move around a bit in use. The slight movement works on the nuts over time, gradually loosening them. Many new plastic seats come with double-sided foam tape that is supposed to prevent this movement, but the adhesive layer soon fails when it is exposed to cleaning chemicals, and then the nuts come loose in short order.
To avoid the aggravation of having to frequently re-tighten the nuts, one can fashion bushings that greatly restrict the movement of the nylon bolts in the holes. From your nearest auto parts store, obtain a few inches of rubber fuel hose of an appropriate size, depending on the bolt diameter, and with a sharp serrated bread knife cut a slice that is about the thickness of the ceramic where the bolt passes through the hole in the china bowl. If the fuel hose is oversize for the hole in the bowl, you can cut a segment out of it to change it from an "O" shape to a "C" shape. Reassemble the seat on the toilet, snug up the nuts as usual and you're done! You may not have to touch the toilet seat hardware for years, until you're ready to replace the seat or remodel the bathroom.