For water and sewage, you always want to connect them directly to the grid and not through each other. So it should look like this:
https://steamcommunity.com/sharedfiles/filedetails/?id=2223944780
Connecting like this will cause problems:
https://steamcommunity.com/sharedfiles/filedetails/?id=2223945379
https://steamcommunity.com/sharedfiles/filedetails/?id=2223944780
Connecting like this will cause problems:
https://steamcommunity.com/sharedfiles/filedetails/?id=2223945379