UV light placement?

[Cash]

I am trying to find out the best placement for a UV light.
A couple options I am considering are
Inline on the return pump.
A separate pump in the sump to the light and return back to the sump. (This is the way I would like to run it so it is not visible in the DT, just not sure if it is efficient that way.)
Or drop a PW/pump in the DT and run through the light and back to the DT.

Thanks for any input

And a BIG thanks to ReeferRob for the light.