Used on the inside of the filter to connect the filter to the multiport valve. A PVC fitting tank adaptor is a type of fitting that is used to connect a PVC pipe to a tank or other container. The female part of the fitting is a socket that is designed to receive the male end of a PVC pipe. The fitting is made of polyvinyl chloride (PVC), which is a strong, durable, and corrosion-resistant material that is commonly used in plumbing and water supply systems. The fitting is typically used in applications where a PVC pipe needs to be connected to a tank or container that is made of a different material, such as metal or plastic. The fitting is typically secured in place using solvent cement or other adhesives.