Auggie is also a 'dunker' but I've gotten him away from making really chunky soup (so I only have to change his water once or twice a day).
The most important step I took was to move his water dish to the opposite side of the cage from his food. This also gets him moving a bit more - he has to take pieces of food one at a time, carry them across the cage (its a big cage, this involves much climbing), dunk the food, eat it, and repeat. The water still gets mucked up, but when his water was next to his food he'd just take several pieces of food, throw them ALL in the water, THEN decide if he actually wanted to eat all of them.
Now I change his water in the morning, and by evening it has a bit of color and some some crumbs floating in it, but it is not a bucket of paste.
I have, also put a water bottle (lick bottle, gerbil style, whatever you call it) next to his food. Sometimes he'll eat the food dry and take a few licks on that.
But no matter what you do most birds will continue to make 'soup'. To me it was helpful though to slow the process a bit.