Three pipes from tank.
Fill, supply, and bleed.
Bleed….constant slope to prevent airlock mounted in the middle rear to prevent water washing out during cornering under tow. Outlet of bleed is below fill point, and so drains from bleed when tank is being filled, allows air in during water use.
Supply…… has a T and tap to drain tank when reqd.
Fill ….. lare diameter for fast filling.
Grey water (red tap) obtained from RV store. Hose fitting next to it is not reqd, for cold shower or general use and T’d into tap supply.
I recon the hand pump you sujested would be a great idea and more than adequate.
I’m only 5’4 so just check you’ll have room for your feet and put plumbing as outboard as practical, caution the tap doesn’t interfere with the closed galley hatch and you should be sweet.
Hope this helps.