Your contents will never evaporate due to the sealing property of the polyseal. Just remove the cap and the needle and polyseal will protect the contents while still allowing you to use it. When finished, insert cap into handle and close the bottle.
** Warning: This product can expose you to chemicals including Lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov