Please note: because these use a natural rubber in the stopper, it leaches oil. To help avoid the stopper falling out over time, take a small amount of rubbing alcohol and apply it to the opening of the feeder as well as around the stopper, this will help dry out the oil. This can be done somewhat frequently, or as needed. When filling the feeder, make sure to turn the feeder upside down, fill, then press in hard and slightly twist the stopper into place, then move the feeder to right-side up. Lastly, as the feeder empties, the vacuum seal can be lost, refill the feeder as needed to ensure no nectar is lost.