Instructions:
  1. Simply slide the white nut over the pipe first, then the red/orange/white nylon washer before the pointed black rubber washer
  2. Make sure that the black rubber washer is pointing the thin end towards the white fitting you have yet to put on and slide the rubber on an inch or so 
  3. Push the rest of the fitting on so that the rubber joins up with the plastic fitting, you may then try and push the fitting with the rubber further down the pipe if need be
  4. Finally bring the nut back and screw onto the rest of the fitting, compressing the pointed washer against the plastic to make a seal, then repeat the action for the other side and that's it!