I am not 100% sure what you you are calling “return” since your title refers to PB sleeve but I will give you a simple explanation for the flow path that hopefully helps.
Flow originates at the pump (of course). It then will go into a valve. That flow will go through the open center valve and then out of a power beyond port and to the next valve into the power in port, through the valve and out the power beyond port and then to the tractor internal 3point valve and dumps into the tractor sump. There can be any number of valves in the chain but the three point has to be the terminal valve. This chain can not have any TEEs in this chain.
Each valve will also have a tank return port (excluding the three point valve). This is the return line from the cylinders that the valves control. One side of the cylinder gets fed pressure and moves the rod piston towards the other side and forces fluid out the other hose. That goes into the valve tank return port and needs to be dumped back to the sump. These tank return lines can all be TEEd together to end up as a single hose to the sump.
On my tractor (L185) similar to your L175 there is a port on top of the transmission case that can be used for this tank return line. Here is a color coded picture of how my tractor is plumbed.
The green is tank return. The red hard line is pressure fed from pump. The red hose is pressure to the valve. The blue hose is power beyond from the valve. The blue hard line is going to the three point valve.
Hope this helps and is not too pedantic or basic. I just want you to be aware that there are two independent paths to return fluid to the sump.