Look at the edstrom guide on RBI, in his S design, there is line going from the bottom back to the top.

Also, what are your thoughts on not using an S system. We are using a 6 cement tub rack, so only 1 column of tubs, an S system seems pretty wasteful. I am thinking of running the line straight down one of the sides with T fittings at each level to lead either directly to the valve, or to an L fitting in the middle of the rack, leading to the valve. I am planning on putting a drain valve on the end also.

So, before I ask any more questions, do you think this non-S design will work, or is an S system really the way to go.