Hi You already have the cistern installed, do not complicate your life. Feed everything from the upper tank. Reasons, 1 ° If there is good network pressure, the tank would not work, over time the water is no longer potable and it is inconvenient to send it to the upper tank. 2 ° To be able to use both systems with a single pipe you have to put several check valves A) at the entrance so that the water does not go to the street when there is no pressure B) in the tank manifold, so that the tank do not fill in its lower part and overflow (the float would be disabled) 3rd. The pressure of the network is not constant (depends on consumption) and most of the time you will not be able to bathe (for example) especially in summer 4 ° You will have to always be aware of the conditions of the network to close or open the corresponding keys as appropriate. Definitely: Having the tank and the lift pump would not use the direct network. regards Pd if something is not clear to you ....... "your question does not bother"