In brief: The best practice for disposing of organic waste is to transfer it to an appropriately labelled bottle for collection by a licenced waste disposal contractor. If the experimental procedure involves washing the ester reaction mixture with sodium carbonate solution, then any gas generated in the stored mixture is likely to be carbon dioxide produced from the reaction of the sodium carbonate and the acid catalyst or unreacted carboxylic acid.
Best practice would be to store the organic layer in a separate bottle from the aqueous layer. However, if the layers are difficult to separate, then it would be reasonable to transfer both layers to the same waste bottle. Glassware which is contaminated with any of the organic compounds used or produced can be rinsed with a small amount of ethanol with the rinse solution being added to the organic waste bottle.
While it is not prohibited in Australia to evaporate volatile waste in a fume cupboard, it is not considered best practice, as this introduces untreated waste into the atmosphere (this method of waste disposal is prohibited in the U.S.A.).
Please see the general answer to ester disposal for further information at this link: organic chemistry.