For recreational boats, I think not regulated for DIESEL... examples:
Comparison of USCG vs. NMMA regs: http://www.generalsportshows.com/certification/about/chart.asp\
http://georgebuehler.com/Fuel%20tank%20drains.html
AS FOR DRAINS IN THE TANK:
Q. Can a diesel fuel tank have openings below the top of the tank?
A. Yes; ABYC Standard H-33, Diesel Fuel Systems is silent on the issue of location of diesel fuel tank openings and therefore does not prohibit openings below the top of the tank.
http://www.abycinc.org/committees/faq.cfm