We are all well aware that whales, sea lions and the multitude of fish relieve themselves in the Ocean. The difference is that we have a choice. It was only a day excursion, and one of the dives was in a marine protected area. Even diluted, the discharge was directly under the entry gate to the water. Absolutely nasty.
I think I will send a note to the dive operator and ask for them to reconsider how they handle waste while divers are in the water or while the boat is moored especially in an MLPA. Also maybe they have a more sophisticated MSD than what it appears to be. Still seems like a very odd thing to do once anchored.
Okay, the real issues here are:
1- You seem to think the boat should bottle up poo.... did you use the head? Did you bag your poo ?
2- Maybe they could install a macerator. This is akin to a garbage disposal and it "grinds" the sewage.
3- Waste regulations are specific to the size of the boat, location of the boat, and in some cases local regulations. As a general rule, a small boat (less than 6 paying passengers) outside of 3 miles from shore (not the island) can do what it wants with regards to poo. Now, California may have some specific regulations with regards to it's marine sanctuaries. It will be a "no-discharge" zone if you want to research it.
Fast visit to Google suggests it may have been.... It will come down to which island you were at.
Current No-Discharge Areas via EPA site:
http://www.epa.gov/owow/oceans/vessel_sewage/vsdnozone.html
4- Different boats are equipped with different types of devices..... Very quickly they are called MSD Or Marine Sanitation Device and fall into "classes".
A type 1 device treats the sewage in a manner that renders it sterile. This would be something like a ElectroSan. ElectroSan generates chlorine from the salt in the water using a small amount of electricity (relatively speaking). It grinds up the toilet paper and sewage.
A type 2 device (if I recall right, because these are rare as heck) uses chemicals to sterilize the sewage.
Most boats are equipped with a regular "head" (finicky marine toilet) that is connected via a Y valve to a holding tank and a overboard discharge valve. The Y valve can be locked to prevent discharge. Tanks are finite in size and the average "use" is about 1 gallon.
Other Marine trivia.... Marine toilets are extraordinarily finicky and small. If you couldn't swallow it, don't flush it. The working "limit" is about 4 pieces of toilet paper (aka 4 squares) plus your "deposit" per single flush. Anything more runs the risk of clogging the head. The passages are at most 1.5 inches in diameter and have flapper valves that are sometimes smaller. It's easy to jam them and unpleasant to take them apart for repair.
As for the contents of sewage... the real issue is that the bacteria can be a tad nasty in human sewage. Beyond that, the contents are a non issue. Bacteria and organisms in the ocean will enjoy the meal. In some areas of the Carribean fish will eat the poo.
Maceration is the recommended minimum as it grinds up the tp and poo.
Practically speaking, it's nearly impossible to enforce this. This is sorta like a diver who touches coral or harasses fish. The difference is that there are marine police and if they catch you it is a big fine. However, they have alot more important things to do then check for stray toilet paper from your boat.
