The McAlpine WC-BP1 is a plumbing connector that is designed to connect a 3½ inch (90mm) diameter outlet from a toilet bowl to a 4 inch (110mm) diameter soil pipe. The connector features an 'O' seal socket, which provides a watertight seal to prevent leaks. To use the McAlpine WC-BP1 connector, you would first need to ensure that the toilet bowl outlet and the soil pipe are both clean and free from any debris or obstructions. Next, you would insert the connector into the toilet bowl outlet, making sure that it fits securely and snugly. The 'O' seal socket should create a watertight seal.