Advice? Two 10 gallon Tanks

I have been toying with the idea of setting up two 10gallon tanks, right next to, or nearby but I wasn't sure on the best way to plumb both systems together. Anyone have any suggestions?

I wanted to run two species specific tank setups without using a divider in a larger tank. I think I could go for a wider diversity range by using actual separate aquariums.

 

Had some time this afternoon to think about this idea some more. Thinking I should line them up side by side, then plumb an overflow into the side of each and have each one drain into a communal sump. Is there a suggested size for small thin tanks?