Bad over sight snowballs to big problem

[Lofus]

Why would you not put a T in the return line outside the tank with a riser to above the water level. Then put a breather valve on the riser. These are basically check valves that allow air into the pipe but no water out. They are designed to be siphon breaks in drain systems.

so it basically looks like this:

Riser & breather valve
|
|--- To bulkhead
|
from pump