My son has a Mic key g tube which is just a button with water filled balloon on inside to hold in place. Your tube is probably falling out because sometimes the water in the balloon deflates. You will have to add water with a small 5cc syringe (comes in the box with the button) which screws into the port on the side of the button. The balloon should hold about 4 or 5 CC's of water. Since you can't see how much water is still in it we just add water slowly until button feels right again. If keeps falling out balloon may have hole in it and just needs new button. We change our son's about every 6 months.