With my rack I modified the design by adding a 2nd set of vertical legs. The rails that the tubs slide on attach to these legs rather than the ones at the front. That way the tub comes off the rails before the back of the tub hits the valve. With this design the valves for the water system do not interfere with the tubs at all. The 2nd set of legs also add additional structural stability.
For the water system I followed the RBI guide here: http://www.reptilebasics.com/edstrom-buying-guide
And here: http://www.reptilebasics.com/edstrom-installation
Glad I could help!