Keep Them Closed
Use a sturdy bottle with a screw top lid. A screw top lid does not leak and minimizes evaporation.Bottles with rubber stoppers, milk jugs with plastic snap lids, and parafilm covered test tubes are not acceptable - their contents can still spill or evaporate.
Close containers tightly, except when adding or removing material. Make it a good habit.
Use funnels?
Funnels with tightly closing lids are available for a wide variety of containers. Use these instead of open funnels for frequently used bottles, and remember to close the funnel when not using it.
A funnel can be left open in a waste container for 30 to 60 seconds after adding waste to allow for proper draining. After that, it must be removed and the lid replaced.