Yes to the loc-line. When the the water drains to the hole, it stops the siphon. All of my return lines(3) have 1/8" holes drilled about 1/2" below water level in tank. Tank drains to this level, if no holes it would drain another 4 or 5" of DT's water to sump. You may want to do a dry(wet) run, with loc-lines where you want them, outside if possible and see what happens when you cut the power. Just a little extra insurance, hopefully not a claim.
Matt