IMO, its not that much of a big deal were you pull and dump the UV..whatever is convenant for serviceing or space for it, ect......But would consider what alimal said about the mechanical filter. UVs can get a dirty build up of detritus from the slow flow. Many do T the drain with a valve to control flow to feed a UV ( saves an extra pump )
Also algae spores can originate from a lighted tank and fuge so might consider pulling from the end of the fuge and dump into the return pump chamber.