OK-I got it now. Issues on removing of water from shower pan. Cant use gravity-the shower pan gets to high. Pumps-they would run dry and surge on and off-plus, one would need to add a switch to turn pump on. Issues with hairs too.
Solution-gravity water from shower pan and sink above into the curb that supports the sink cabinet. Its big and would allow lots of accumulation. A boat bilge pump will be placed inside of surge tank-due to volume of tank, the bilge pump will do little cycling. Plus-its all automatic. Bilge pumps are inexpensive too. They can work with sort of dirty water and can work in very shallow water levels. No switch to turn on. Water will be pumped from surge tank to holding tank.
I am going to have bottom of curb filled in with a plate-will make a top with hinged cover that allows for clean out and pump inspection.
Attwood has one for about 100 bucks-its plastic, but has the inlets up to high. Reviews are not so good on this unit. A decent small bilge is about 40 bucks.
Pete