This item is often forgotten about but it is an important part of any solar system. If the solar panels should ever over-heat and the pressure builds in the system past the safety threshold, the pressure relief valve on the solar pumpstation will open up and let a small amount of fluid out to relieve the pressure. This fluid has to be collected somewhere and this unit is perfect for that purpose. Also if there is any antifreeze present in a solar collection vessel it must be visible. If so this is a good indication that the solar system needs maintenance work.