Just my 2cents - i do not plumb anything on return.
Yes plumbing looks easy and some pros like not using extra pump, Hovewer for me lots of downsides:
- my in sump refugium creatures who made into return would be going through UV and back to sump
- if I feed automated frozen while on vacation using return pump if will not be possible obviously
- i will have to fine tune manifold and any little clogs might change the amount of water going into display, meaning yes I will hear it because of emergency overflow and be safe, but I do not like to be in this situation, because reasons for this are plenty and checking which one will be difficult
Instead I would run one extra pipe going into Carbon and UV after for example or another GFO or Algae reactor with return back into sump.
Sure also cons to this method but for some reason it seems more logical.
Just my 2cents.