Sump piping

[e46er]

3/4" return should be plenty for a tank that size

a 1" drain would be ok unless you plan on keeping large snails which could potentially block it

a mag 350 puts out ~ 200 GPH @ 6 ' head pressure so a 1" drain would have to be almost clogged solid to cause a flood
id drill 2 holes and do a herbie style overflow silent and virtually flood proof
return(s) over the back of tank