Boiling water of course
you can try and put boiling hot water down the drain, but be careful It depends on how far the wax went before it solidified. You might be able to get by with just removing the sink "P" trap, cleaning it and putting it back. If the wax solidified later in the pipe, you'll need to run a "snake" through the pipe to break loose the wax. A snake is just a device for running down the drain to break loose junk that got stuck.
because its not a liquid its a solid
Solvent wax refers to solvents that remove wax. The solvent is able to dissolve, or get rid of, the wax.
Yes
Float.
yes.
Yes
No, it floats. Try it.
floats
The gravel will float and the wax beads will sink
Each of the three substances have a trait that makes them unique from the other two. By using this trait, you can seeperate them from each other. The wax, for example, has a low melting point. The salt will dissolve in water. If you start by heating the wax-sand-salt mix, until it has liquefied, then put it into boiling water, the wax should float, the salt should dissolve, and the sand should sink. As long as you can mix the wax around enough in a semi-liquid state to get the salt and sand free, you should be good.
the shift in weight from the new tank may have caused a shift in the wax ring and gasket where your toilet hits the drain pipe. wax rings only cost about $3-$5 and are easy to replace with a friend.