I pre drilled a 3/4” board with three 1 3/8” holes for the drain line to be secured. I then screwed the board to the 1” plywood that is in between the tank and metal stand.
This is the best pic I have. You can see the three 1” black pvc running through the board.
Then on the return manifold I put another 3/4” plywood the I used pvc pipe clips to hold the pipe in place