I would avoid it as the bags have a HUGE surface area.

If you've ever used a "machine" pipe for smoking various vaporisable goods, you might have noticed there would be a large dose of residue on the steel wool. Even if a person had loaded a single hit onto very clean steel wool and blasted the whole thing, you could wait a few days or months and take a hit from that again and it would be very potent.

Now how about that effect occuring across a huge surface area?

OFC you could do the alcohol method as recommended above. It's not a significant reason to avoid using the volcano but the loss would definitely be pretty sizeable if you did not take a hit immediately as it vaporised.