Well, duh, on having bad things happen if the line breaks. I don't recall saying anything about monitoring it, either. Again, duh.
Looking at my setup, it seems that having the return hose go through the drain plug means the hose has to have some part of it below the oil pan in order to negotiate that. It would seem to be safer having it tapped in to the side of the oil pan.
On my 1982 300SD, I only have the single canister filter.
1987 300SDL 265,000 mi.
1982 300SD 325,000 mi. (and holding)
1956 Packard Clipper 150,000 mi.