I have 6 pool returns. Return 1 & 2 work, 3 doesn't work, 4 works, 5 doesn't work and 6 has low water pressure.

I've used a bladder in all of the returns but other than some debis coming out, the two returns are still clogged.

I tried using a drain snake inside the returns, but no luck. I plan on inserting the snake inside the return line where the  equipment is located.

What I don't understand is why every other return line is clogged. Aren't all of the line hooked up in series?