Ummm, I've been toying with the top being my inlet using a Koolance 4-way nozzle body
Left - return from blocks
Right - capped
Top - fillport with Koolance Ball Valve
Bottom - where the metal tube is, fluid into the loop
My thought on connecting the valve to the top section of the 4-way nozzle body is to prevent back flow up into the fillport tubing.