The ShowerPowerBooster uses standard compression joints which squeezes a brass compression olive to create a seal and prevent leaks. You will find a mesh held in by a rubber surround on the upstream side of the ShowerPowerBooster. The purpose of the mesh is to protect the pump from debris and the rubber is to hold this mesh in place. It has nothing to do with sealing the pipe.
The image above shows:- 1.0 Shower Power Booster Thread – 2.0 Filter – 3.0 Brass Compression Olive – 4.0 Nut to compress olive.
If you are using copper pipes you do not need inserts but refer to our guide to making a leak free compression joint with this link
For all plastic pipes you should also use inserts:-