I’m a little confused and maybe my older tank is designed differently than yours. I have a West Coast 2003 with the stock tank and an added tank. On the stock tank there is the center pipe that threads into the drain. There are side holes in the lower threaded rubber area of the pipe, designed to allow some drainage to clear scales and other debris from the bottom of the tank while circulating. Depending on how far you screw it in, you can vary the amount of drainage you will get from the bottom. If bait is getting sucked into the lower part of the drain pipe, you need to screw the pipe down more to lessen lower drainage.
I’ve found the stock tank to perform pretty darn well and definitely keeps the bait moving in circles.