As to the borax, I just played around with heating and recharging the solution as a way to get some impressive crystals to grow a bit faster. My own impatience aside, young students like to see results quickly. When you get results that can be clearly seen the next day and can be seen daily, their interest stays high. It helps keep them actively involved and focused on some other crystals and growing methods that take a bit more time. 20 Mule Team is also readily available and quite inexpensive.
Any leftovers can just go into the washing machine.
If you haven't read the Rock Net FAQ and User Tips yet, now would be a good time to do so.