This is a branded Blue Magic draining adaptor as sold thousands and thousands of times in the world markets.
When moving a waterbed it is vital not to disturb the inner fleece layers. This can only be achieved by thoroughly draining the waterbed so that it is almost empty. If the bed is moved before the bed is properly drained then the fleece layers will move and the bed will be damaged.
To drain properly it is essential to achieve an airtight ( and watertight ) seal with the draining hose. This adaptor provides such an airtight seal - just connect it to a standard hose using a quick release screw fitting or similar and drain as per manufacturers instructions.