That would be against ABYS & USCG specifications.
Marine tanks cant have any 'outlet' lower than the top of the tank ...
leakage considerations.
A surveyor would have a heart attack in finding a tank with a 'bottom
tank', your insurance carrier would probably 'not allow' any claim that
resulted in a faulty bottom tap. The CG wouldnt care ... the fine is
the same if you pumped or inadvertantly dumped the oil.

Use a separate 'dip tube' all the way to the bottom for water suction.
OR ... use a 'water knock out pot' as the first stage in the fuel
filtering system ... just an empty filter housing with a bottom tap
thats attached to clear (tygon, etc.) tube. Most of the water will
gravimetrically settle in the 'knockout pot'. When you see water in
the tube you drain it.

:-)


In article , Roger Long
wrote:

I have about 12 inches of clearance under my aluminum tank, a highly unusual
configuration. On my list of big projects is to cut into the flat bottom
and attach a big sump for water and other crud to sink into. It's a nutty
design with a big flat bottom so there is no sump point but it probably
keeps any stuff in the bottom of the tank swirling around in suspension so
it goes through the filters bit by bit. The suction is in the center so
unlikely to pick up much. Maybe it isn't such a bad design after all.