Every basin requires a waste trap to connect from the basin waste to the pipe which carries your wastewater to the drain. The bottle trap, also known as a basin trap is one of the many types of connectors designed for this purpose. The bottle trap is cleverly designed to retain a small amount of water, which stops smells from the drains passing back up through the basin into the bathroom.
The bottle trap is available in simple white plastic, polished chrome or even brass effect. The latter two would usually be used when the bottle trap would be visible. For example, when fitted to a wall mounted basin which has no pedestal to cover the pipes and waste fittings.