lolz @greenrun cos no one would ever imagine how it would look like seeing manufacturers produce a rectangular tanker? however its an idea what considering. however you should consider the roads this rectangular tankers would use, for if they are rectangular in shape, it would be needing a different road construction to fit its new shape as well.
for me i believe to much is at stake for a rectangular tanker
We already have a rectangular box truck, so a rectangular truck tanker won't look so much out of place :)