coming from the guy with no tanks larger then 100 gallons lol.
lungfish aren't my forte, but as a general rule, you want a tank to be atleast as wide as the fish is long, and about 3 times as long as the fish is long. for a lungfish you'd probably want an 8'x3'x2' (lxwxh) which is about 360 gallons, or 1360 liters.......of course lungfish don't move an awful lot.