The Splicer is machined with a left-handed thread in one end and a right-hand thread in the other end. This enables you to screw onto two pieces of pipe at the same time.
Measure the internal thread length and mark the two pieces you wish to join together. Apply thread sealant or anti-seize to both ends of the polypipe and to the inside threads of the Splicer. Identify the right-hand on the Splicer. Start both pieces into the Splicer and turn the RH thread to the right. This will pull the LH thread end into Splicer at the same time.