The slush mixture makes approximately 1 gallon. Once you mix it with soda it will make 2 total gallons. Start by preparing two half-gallon containers that you will use for freezing. You can mix everything in a huge bowl if you have one or divide it as you go and mix it individually in your two containers.
Microwave water until very warm. Pour in blender, add sugar and blend until sugar is dissolved. Add 6 oz orange juice concentrate and lemon juice to blender and blend on high until totally smooth. Add contents of blender to the huge mixing bowl.
Add half the bananas and half of the pineapple juice to the blender. Blend on high until smooth. Add contents of the blender to the mixing bowl.
Add remaining bananas and pineapple juice to the blender. Blend until smooth. Add to mixing bowl.
Mix juices until totally combined. Pour into your freezing containers and close them tightly. Freeze about 24 hours until frozen solid.
Remove ½ gallon frozen slush mixture 1 hour before you are serving it. After letting it thaw on the counter for an hour, use a table knife to cut it in two directions. I normally cut it into about ½ inch sections. Add 1 2-liter soda to a gallon pitcher. Spoon slush mixture into pitcher. Stir gently to combine. Adding the soda first reduces the amount of foam in your pitcher.
Repeat previous step if you are making the whole recipe at once. This can also be made in a 2-gallon punch bowl instead of in 2 gallon pitchers.