To freshen your bathroom, every time you change the toilet paper roll, pour a few drops onto the inside cardboard of the roll. This is much easier to do if you do it before actually putting the roll onto the toilet paper holder.
Now, every time somebody uses the toilet paper, the oil will be stirred up into the air a bit and release the fresh scent of whatever oil you chose. We prefer lemongrass or lemon at our house, but you might prefer to use lavender, grapefruit, or peppermint. You can even keep several on hand and switch off!