To prevent water from coming into the cake during the cooking process, I recommend you to wrap each log with plastic wrap and then double wrap with aluminum foil on the outside before boiling them in water.
Use a big soup pot, and put the cake vertically (preferred) or horizontally, depending on the size of your pool. Fill the pot with water and ensure all the banana cakes are entirely submerged under water (ideally at least 2 inches).
Bring to boil, cover the pot, and adjust the heat, so the water is still hard-boiling but not spilling all over the place.
Check the pot and fill it with hot-boiling water if the water level drops below the cakes every 1.5 hours.
The banana cakes (bánh tét chuối) should be made after 4 hours or 5 hours; you’ll be able to smell the banana and coconut milk at this point.
Discard the plastic wrap and aluminum foil. Let the cakes cool down to room temperature approximately 2 hours before serving.