I have similar problem. I changed the 1ft line from the city inlet to the main/water pump- theres a T fitting on the pump. Then line goes to toilet, then shower, sink, and back kitchen. After I replaced line I lost pressure to toilet, but nowhere else. Also, may have accidentally turned on pump while no fresh water in tank.
Replacing the toilet screen/valve part for 50 bucks but no improvement. Any suggestions? All lines and fittings are correct.