How to make an inflation suit/costume out of trash bags?

Its easy. Lay the bag down and diside what size you need. Make a small hole in the front where you want the belly button. Grap a balloon and cut the bottom out of it. Put the cutted balloon true the belly button hole (with the blow or inflate hole on the outside of the bag). From the inside you make the hole around the balloon closed with duct-tape( make sure no air can escape around the bellybutton hole). Grap the bag and close the open topside tottally (airtight).

Watch for an old shirt or dress for you suit. Cut a small hole the shirt/dress on the bellybutton. Now you can put your bag under the shirt/dress. And put your balloon blowhole treu the bellybutton hole of the shirt/dress. You can connect a balloon pump to it and its time to inflate.

A small tip. You can also use duct-tape to make the better shape.  Fold the corners of the bag on the back and duct-tape it so it stay there. This make it more realistic looking (like a pregnancy belly)