It goes under the flange and transfers the load of the flange and toilet and you out onto more solid surrounding wood.
Floor sagging under toilet.
Take out the floor bolts at the base of the toilet using a wrench.
The raising of the toilet causes it to rock from side to side.
Disconnect the water line using your wrench or pliers.
Underneath the toilet base is a round toilet flange that connects the toilet to the drain pipe.
Toilets usually rock because they are not resting flush against the floor.
If the subfloor is spongy under your leaking toilet the toilet may have started to wobble and the problem is quickly going to get worse unless you make a fairly major repair.
Then you can start the floor repair and toilet and tub.
If the toilet flange the round item that sits under the toilet and connects the toilet to the drain pipe is higher than the floor the toilet becomes raised.
Turn off the water supply to the toilet at the wall.
Follow the easy instructions that come with your product being sure to tighten each of the four bolts a little at a time so the rubber gasket goes down evenly around the bend pipe.
Just make sure the flange is flush tight with the top of the floor otherwise your toilet will wobble.
And cut the floor out and start replaceing with plywood set a skill saw at a deapth that it wil cut through the old floor but not into the joist.
Flush it several times to empty if of all water.
If it is only the floor then remove the toilet and the tub.
Usually the cause of a wobbly toilet is that it is not sitting flush against the floor.
Replacing a wax ring or even the entire toilet is easier than replacing the subfloor under a toilet.