Hi, I've been spending some time refreshing the holding tank on our Horizon 76 MY, including a complete pump out, new dip tubes, new SCAD monitor, etc. As purchased, the setup looked something like this: The lettered devices are check valves. The output flapper on the pump ("B") was rotted and nearly completely missing. And the vent check valve ("D") was inoperative (allowing two-way flow). I purchased a rebuild kit for the pump, so it's working again, and have replaced "D" with new. (My guess is that the previous owner added "C" to compensate for "B" being broken.) To my question: Are check valves "C" and/or "E" a good idea or are they just adding unnecessary restrictions to the path overboard? Thanks!