I have been trying to avoided this thread but having testified before a House subcommittee on Type III MSDs I have done quite a bit of research on the subject.
I must say there is no safe place to dump a full holding tank anywhere between the North and South Drops. There are no operable pump out facilities on Tortola because anything that passes through them is discharged with virtually no treatment about 400 yards off Slaney Point along with 80% of the islands other sewage.
To make the best of a bad situation, dilution is the best solution. It is best to leave the tank open to the sea while underway until entering an anchorage then leave it closed until at least 1000 yards off shore in more than 200 feet depth. The reason for the depth is to allow solids to disburse. It will be consumed by bottom feeders. (Remember that when you chow down on some conch fridders or Lobsta ) Fresh water bacterial will be killed off fairly quickly in the ocean. The big problem is nitrogen. Nitrogen stimulates the algae that smothers coral and can persist in strong concentration for miles. Think about your location and the currents before opening the tank. Where will the nitrogen end up? On the Indians? Monkey Point?
-------------------- Travel is fatal to prejudice, bigotry, and narrow-mindedness, and many of our people need it sorely on these accounts. - Mark Twain