1. The membrane case is the reverse osmosis membrane case. 2. It has 2 water outlets. One outlet goes to the reverse osmosis water tank. The other outlet goes to the kitchen drain 3. Normally the membrane case does not need to be changed for many years. However, depending on the quality of the water and especially the filters, in some cases it fills with dirt that is not easily cleaned. 4. Connects with a 1/4 inch tube. This cross-section is present in all reverse osmosis systems.