http://newboatbuilders.com/docs/H-33_Diesel_2005.pdf

I've quoted some of the sections. As for drains at the bottom see [H]33.5.7 below; and,

For a sight guage, see [H22.3.8.
If you hve a seacock that separates the sight guage at the top and bottom, it would seem without an issue...

33.5.7 Drain valves on filter(s) and fuel tank(s) shall be of the type that cannot be opened
inadvertently, or shall be installed in a manner to guard against inadvertent opening. All other outlets for
draining fuel from the system are prohibited.
33.5.8 A means to determine fuel level or quantity shall be provided.
33.5.8.1 If a sight gauge is used;
33.5.8.1.1 it shall be equipped with a shutoff valve at the top and at the bottom of the gauge, and
33.5.8.1.2 a warning label shall be placed adjacent to the sight gauge, and
33.5.8.1.2.1 the warning label shall comply with the requirements of H-33.16.