ive done it when i was out of juice. it wasnt bad the first time but once you have gone through more then one cycling i have found it to be NASTY. ( recycled recycled e-juice if you will. ) i also used this method ( when i was low on juice ) to extract the juice from the free pre-filled carts that came with my 510 and then cut that juice to something useable which worked out well and extended my vaping till my new juice arrived 