Basically there is no return line. The pressure line runs through one side of the block, through the power steering valve, then back through the other side of the block. The outlet under the seat, at least on my 7100HST, is an auxiliary outlet, one way, that is controlled by the directional valve under the front of the seat. Oil pressure is only used by the steering valve when you are turning, at least the way I understand it. I am trying to attach a PDF file with a parts breakdown for a Kubota LA352 loader. Page 17, I think, shows the hydraulic block that you will need.
I think my third picture on my original post shows the hydraulic block front cover plate that provides for access to the pressure side of the hydraulic oil supply.