One thing I'd recommend on the setup you drew was two separate manifolds for your mixing pump. One manifold on the suction, one on the discharge. On the suction manifold, put a line from the 100 G Rubbermaid (waste water), 70 gallon Rubbermaid (mixing and fresh SW makeup) and 65 gallon Rubbermaid (FW for mixing SW). On the discharge manifold put a line to 70 gallon Rubbermaid (SW mixing line) a line to 100 gallon Rubbermaid (fresh SW fill) and a line to waste or sink. Each line needs a separate valve.
I run the exact setup written above and it allows a single pump to do everything with water changes. I change 100 gallons of water out in just a few minutes. Makes life very easy for water changes.
