I am about ready to join the deck/hull of a Petrel for my wife. At her request I need to include a "camel back" type of water bag.

It's not too late to convince her to use the more common setup - a Kokatat 'Tributary' water pack that attaches to the PFD.
Most of the folks in my paddling group use them, partly because the water setup travels with the paddler to different boats. They do work well, though the older models benefited from replacing the bladder with a Platypus BigZip setup.
https://kokatat.com/product/tributary-hydration-system-lvatrb2rd0c

With the 'backpack' setup, you don't have to exert much suction to pull the water through the tube. (Think height difference between the top of the water in the bladder and the mouth...) Perhaps some trials pulling/sucking water from a bladder in a lower position would be useful? Some of the surfski racers use a pressurized system with a water bladder sharing a hard container with an inflated air bladder. Bite on the valve and the water shoots into your mouth.

Whatever system you use, be sure to get a bladder that disconnects from the tube, like the Platypus. The bladder needs to be kept clean, and it's a LOT easier to refill it if you can just carry it to the tap.