2003 Toyota Camry Reserve coolant take emptying & leak

Well it starts out that as you stop, you hear a sloshing sound like a rolling water bottle under the driver's seat. The engine will eventually overheat due to the reserve coolant tank emptying out. There is also a small leak near the back of the head as this is happening now. The first time this happened, we put a brand new engine in, waterpump, thermostat, transmission pump, and hoses. Now with a brand new engine in with less than 2,000 miles on the engine, the car is exhibiting the same problem again. What could be the cause? We are about to install another brand new engine due to the warranty, but we want to keep from having to replace engines on a consistent basis. Any suggestions as to the root of the problem?