After taking the Seakamp heat exchanger off the Universal M25 diesel (again) and getting it repaired, it was about a month before getting it back on the boat. Sometimes a picture is worth a thousand words when you're putting something back together.
Heat Exchanger salt and fresh water circulation system, hose connections
The heat exchanger set up on Reality Check has the Antifreeze/Fresh water plumbed with a bypass valve (behind the bulkhead) to the hot water heater.
Photo diagram descriptions (left side, top to bottom):- Salt water exits the heat exchanger and goes to a vented loop. (exhaust system connections not shown) Another hose from the vented loop goes to the exhaust mixing elbow to cool the exhaust. The salt water is ejected from the boat with the exhaust.
- Salt water from the sea water strainer goes to the salt water pump.
- Antifreeze/Fresh water entrance to the heat exchanger. This hose is the return from the plumbing behind the bulkhead that also goes to the water heater. The connections are hidden behind the bulkhead.
- Salt water from the salt water pump enters the heat exchanger through this hose.
- Heat exchanger zinc is on the bottom of the HX (can't see in this pic)
- Antifreeze/Fresh water exits the heat exchanger and goes up through the fresh water pump, engine block and thermostat back into the manifold. The hose where it comes out of the heat exchanger is hidden under the exhaust flange (in the pic).
- Antifreeze/Fresh water hose from the manifold to the plumbing behind the bulkhead, which also goes to the hot water heater. The return from the plumbing and the hot water heater goes into the heat exchanger to be cooled. The connections to and from the hot water heater are hidden behind the bulkhead.
Seakamp 3" Heat Exchanger hose connection diagram

Seakamp 3 Inch Heat Exchanger hose connections on the Universal M25 Diesel. This part is #302631, not the #299835 CN. The difference in the parts is the angle of the tubes.
Hot water heater bypass valve

Heat Exchanger hot water heater bypass valve (behind the bulkhead).
This valve is OPEN on Reality Check.