From the Beta Marine Engine Forum
"You can disconnect the large hose at the bottom of the heat exchanger tank between the tank and the engine fresh water pump or disconnect the small water heater hose from the bottom of the tank under the exhaust outlet."
More info from the Beta Marine Engine Forum.
"Due to a lower specific gravity, a 40% coolant /60% water, ratio transfers heat more efficiently than does a 50/50 coolant ratio. It still gives more than adequate freeze protection in tropical climates.
My first recommendation would not be distilled water. Use normal tap water that is not "hard" or filtered water. Distilled water lacks any mineral content and has a tendency to attract minerals from its surroundings."
We chose the big hose and at the water pump.
This sounds reasonable and is a proper way to pipe a water heater that is higher than the engine. The accumulator tank vent cap should be he the highest point in the system and provide venting for the entire coolant system with a vent cap rated at ~13 PSI.
The lower vent cap on the engine mounted heat exchanger tank needs to be a higher release pressure. Usually 15-16 PSI.
This means that if all is working as it should be, the vent cap on the engine mounted heat exchanger tank should not open and release pressure (air or water) from the system. All venting will take place at the higher vent cap which has a lower opening pressure.