"In Ontario and other parts of Canada, especially inland waterways, all boats fitted with a marine toilet must also be fitted with a holding tank. This tank stores raw sewage, ("black water"), until it can be properly disposed of at a pump-out station. "Dual" systems, with Y-valves allowing toilet waste to dump overboard, are illegal in Ontario and some other areas. These valves either must be removed, or locked in a position that allows raw sewage to enter the holding tank only. Portable toilets are legal only if they are well fastened to the boat, and have a permanent fixture enabling them to be emptied at a pump-out station." It has been my experience that they do allow US boaters in with ordinary porta pots even when aware of the arrangement. Tod