Leaking bulkead solution?

[daplatapus]

Ya, but it's something you'll never forget now

And yes, your main drain needs to always be completely submerged and low enough that it doesn't create a vortices in your overflow. The other pipe you are using for your safety should be about 1/2" or so lower than the maximum you want your tank level to be at. Not 1/2" lower than water overflowing your tank, but where you want you max height at. I found with mine I actually had to play with that one a bit to find the right height so that: 1) water wasn't running down it all the time,
2) low enough that it would act as a safety and not allow the water height to climb above a certain point even if I had a total blockage of my primary siphon.