Sorry, we got too many lawyers in the US:
USCG Systems Engineering Division (CG-ENG-3)
Your direct discharge head is illegal in the US and you can get fined heftly. My understanding even if you lock your heads seacock shut it is still illegal in the US (US Coast Guard states a permantently installed head must meet their regs).. If you are a foreign boat passing through I think you'll be ok.
This is from the above Coast Guard link:
Vessels having no installed toilet are not subject to the provisions of Section 312 of the Act. Portable toilets or porta-potties that use no installed water, power, etc., are not considered installed toilets and therefore not subject to the requirements in 33 CFR Part 159. However, regulations still exist to prohibit disposal of raw sewage within U.S. territorial waters, the Great Lakes, and navigable rivers. Use of portable toilets in combination with a direct discharge toilet is not permitted. Vessel owners may elect to remove installed toilets and use instead portable toilets. For vessels having a portable toilet, all non-compliant fixed toilets should be removed unless impractical or unsafe in which case such devices should be rendered permanently inoperable. For inspected vessels using portable systems, use only devices manufactured of a durable material, such as molded plastic, aluminum, etc., to facilitate removal ashore, securely fastened to the vessel using straps, wooden framing, or similar materials, and maintained by the vessel operator following the manufacturers instructions as to waste disposal, chemical additives, etc. "
Actually there are some (but not all) porta poties that are Coast Guard approved type III msd.
Porta Potti & Portable Toilets - Wholesale Marine