I am thinking of the following solution, any comments ?

1. Replace the Jabsco Diaphram pump with a Whale Gulper. I believe this
will have two benefits, allow me to eliminate the Pump Guard (Whale
advertises that a pump guard is not needed in a shower application, the
pump can deal directly with the soap & hair), and I hope it's so much
better than the Jabsco that it pulls more of the water out of the boat
before it looses suction.

2. Either eliminate Pump Guard entirely (to get a better vacumm). If
people don't recommend I do that, then maybe I will turn it so that the
water inlet is on top and exit is on bottom, such that I eliminate it
contributing to the water flow back into the shower.

3. Shorten up the lines. They seem longer than then need to be, for
example eliminate the two feet of line running along the floor before
rising up to form the loop. Hoping shorter length may have less
opportunity to store water that can return to shower. This change I am
most aprehensive about ... as the that two length of hose might be
providing a positive benefit, being that it is at or below the level of
the drain and might be helping to increase the capacity of the drain.

4. Or, instead of shortening the lines, I might first create a ramp up,
then loop down per Pete C.s suggestion.

Any thoughts ?