Aluminium tank sounds like an aircraft thingy. Why? Go zinc plated steel
, even stainless steel
, and fit it fir the life of the boat.
Brass Auto-Brake pipe should be good enough but the cost of all this is small, and the loss of fuel at the wrong time too great.
And make it as big as fills the space nicely. You don't have to fill it right up all of the time. Provide an extra set of connections and add a car style filter and electric pump
so you can recirc 'iffy' fuel and check the filter for water
and dust/grit. Pipe tank connections to the low point or sump of the tank. Add a shallow baffle to trap the last pint in the sump/low point.
You'll only do it once so do it right.
Just had to do work on my tank and I'm not happy with what I put back.
Your local industrial parts
supplier will have a wide range of pipe fittings and should have a look up table for 'marine diesel' rated components and they'll be cheaper than a walk in shop. Have fun. Don't forget the soap.