First, make sure that the filter is securely attached to the valve. Attach both the metal parts included in the supporting structure to the mounting holes inside the round plastic part. The metal parts must cross over each other. Pull the white cloth filter over the support structure and fasten it with a rubber band. The rubber band is to be fitted over the recess of the metal parts, not on the plastic part.
Push the valve and filter into the pipe until you can attach them to the mounting frame. Make sure you hear a click. This means the valve has been securely fastened in place.