That sounds like a bad deal, miz ducky. I get mine in big whacking jugs from Lucky Vitamin, a decent online site for all kinds of aromatherapy and homoeopathic supplies. When I checked
their website this morning, they were offering 16 oz bottles for $14.39, about 15 times cheaper than your little bottle. Shipping is additional but as I recall pretty reasonable and the stuff comes very well packed.
(But keep in mind that, like most essential oils, the stuff is lethal if a child drinks it and can cause serious dermatitis if you dump it over on your clothes, which is why it's normally sold in teeny bottles. So if you get a jug this size, you'd want to keep it locked up and take a small bottle -- glass, as it eats most types of plastic -- to refill regularly for your work.)
I should work up a little description of my practice in using it (I've gotten very familiar with it these last weeks), but I'm getting ready for my Cephiro to Campus run. I'll try a new thread sometime later this week. But to answer your immediate question, no, the oil evaporates naturally, so once it's used you only need to air the sketches thoroughly (overnight is sufficient).
It is, however, essential that you get as much of the adhesive off the paper after removing the tape, as this (not the tape itself) is what will continue to damage the paper. A good hint is to use a paper tissue to soak up the softened adhesive until the paper no longer looks shiny or feels sticky.
I once read a downright terrifying description of how someone tried to separate stuck cel layers using one of those infrared heat torches they use to strip old paint. (It did separate the layers, but, IIRC, the top layer sprang straight up into the air and had to be caught before it landed or it would stick again but in a different place.) 
