Sailboat fuel tanks

I am installing a new engine in my Morgan OI41.  Since the main tank
(mounted on the stbd side against the hull) was 30 years old I decided
to replace it.  Had to cut it out in 3 pieces which means that the
replacement has to be made into 3 separate tanks.  I realize that each
of these tanks will need its own vent but I would like to connect the
tanks so that I do not need separate fills and picks up.  In other
words I want to join them with a flow-thru at the bottom so that when
I fill the first tank it flows into the other two.  

This means joining the tanks in some way.  I have a tank builder (in
Miami, Florida) who is proposing to connect them with 1 1/2
connectors.  However he is unable to adequately explain how he
proposes doing this I am hoping that someone in this group has had
experience in replacing (and connecting) replacement tanks.

Any suggestions will be appreciated.

Joe