A bottle assembly comprising: a container having an open end, a closed end, a base portion, and a neck, the neck having a rim defining the open end of the container, wherein the neck of the container comprises external threads thereon; a vent assembly positionable on the rim of the container to enable venting of the container during use; and a collar assembly generally defining a closure for the container, the collar assembly configured for releasable engagement with the neck of the container over the open end thereof, the collar assembly comprising a collar and a nipple held in assembly with the collar, the collar assembly including internal threads for threaded engagement with the neck of the container, wherein the nipple comprises a flange having a bottom face, the bottom face of the flange comprising a plurality of vent features extending radially inward from an outer edge of the flange in equal, circumferentially-spaced relationship with each other, wherein the collar assembly and the container are configured relative to each other to enable selective configuration of the bottle assembly between a first configuration and a second configuration, wherein in the first configuration, the collar assembly is configured to sealingly engage the vent assembly and urge the vent assembly into sealing engagement with the rim of the container, wherein in the second configuration, in which the vent assembly is omitted from the bottle assembly, the collar assembly is configured to sealingly engage the rim of the container, and wherein the plurality of vent features extends radially inward of the rim of the neck of the container but does not extend radially inward of a top of the vent assembly, such that in the first configuration of the bottle assembly the vent assembly sealingly engages the bottom face of the nipple radially inward of the vent features, and such that in the second configuration of the bottle assembly the plurality of vent features engages the rim of the container so that air can enter the container by the plurality of vent features. a container having an open end, a closed end, a base portion, and a neck, the neck having a rim defining the open end of the container, wherein the neck of the container comprises external threads thereon; a vent assembly positionable on the rim of the container to enable venting of the container during use; and a collar assembly generally defining a closure for the container, the collar assembly configured for releasable engagement with the neck of the container over the open end thereof, the collar assembly comprising a collar and a nipple held in assembly with the collar, the collar assembly including internal threads for threaded engagement with the neck of the container, wherein the nipple comprises a flange having a bottom face, the bottom face of the flange comprising a plurality of vent features extending radially inward from an outer edge of the flange in equal, circumferentially-spaced relationship with each other, wherein the collar assembly and the container are configured relative to each other to enable selective configuration of the bottle assembly between a first configuration and a second configuration, wherein in the first configuration, the collar assembly is configured to sealingly engage the vent assembly and urge the vent assembly into sealing engagement with the rim of the container, wherein in the second configuration, in which the vent assembly is omitted from the bottle assembly, the collar assembly is configured to sealingly engage the rim of the container, and wherein the plurality of vent features extends radially inward of the rim of the neck of the container but does not extend radially inward of a top of the vent assembly, such that in the first configuration of the bottle assembly the vent assembly sealingly engages the bottom face of the nipple radially inward of the vent features, and such that in the second configuration of the bottle assembly the plurality of vent features engages the rim of the container so that air can enter the container by the plurality of vent features.