These balls come in all sizes, so you want to choose one that's not too small or too enormous. The "standard" beach ball size will likely work best for this project. Blow into the air spigot, making sure not to let any air escape, until the ball is about half to three-quarters of the way inflated. You can adjust this to how big you want your belly to be. If you want a huge belly, then go ahead and inflate the ball all the way. It will look cartoonishly large for a pregnancy, but that might be what you're going for with your costume. Again, you can use ace bandages, bandeaus, or tank tops to do this. Because a beach ball doesn't have nearly as much weight as a helmet or two blankets, you won't have to work so hard to keep it in place a single tight bandeau or tank top should do the trick. Make sure to point the air nozzle down toward the ground. If it points out or up, it will be noticeable through your shirt, and if it points back toward you, it will irritate your skin and start hurting after a little while. With this method, you might even be able to get away with a tighter shirt! Try out a few different shirts and see which one goes best with your fake belly.
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One-sentence summary -- Choose a beach ball that's appropriately sized. Inflate the beach ball about half-way. Secure the beach ball to your torso. Wear a loose-fitting shirt over top the beach ball, and you're ready to go.

If you have a Canon printer which uses a FINE cartridge like in the MX or MG series, you will have a center paper output cover which is above your output tray. Open your ink tray in the center which is above the output tray. Make sure that your printer is plugged in and turned on. In order for the ink compartments to slide into view, your printer must be powered on. The ink cartridges will slide to the right side of your open tray. This is the replacement position. In some Canon printers, such as the MX or MG Series which uses FINE ink cartridges, the cartridge holder moves to a replacement position behind the head cover. The head cover will open automatically. If you have a Canon PIXMA printer which uses several, smaller ink cartridges, the cartridge holder will slide into the middle of your operations tray when you open the operation lid on top of the printer. If there are already ink cartridges in your printer, you will have to remove these old ones. Press down on the ink cartridge you want to remove. The cartridge lock lever will click, dislodging the cartridge. Once you hear the click and see the existing ink cartridge popped out, pull it the rest of the way out. Take the new cartridge from its packaging and remove the protective tape. Some Canon printers only use two cartridges, one black, and one tri-color, such as in the MX series. Others like the PIXMA use several cartridges, one for each color. All cartridges will have a protective film over the ink nozzle you need to remove. Remove the protective tab on the ink cartridge. This is a plastic film that covers the part of your cartridge which dispels the ink. Be careful not to touch the copper-colored area of the cartridge or the ink nozzles. touching this area can cause clogs, ink failure, or a disconnection if your fingerprints smudge the area. Do not shake your cartridges either. Gently slide the new cartridge into the ink slot. Insert your cartridge into the slot with the ink nozzles facing away from you. The color cartridge(s) goes on the left side. The black cartridge on the right side. Make sure you hear a click to ensure the cartridge is locked into place. You should feel it click into place. Once the door is closed properly you will hear the cartridges slide back into place. Finished.
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One-sentence summary --
Open the ink tray in the center of your printer. Remove any existing ink cartridges from the printer. Remove the new ink cartridge from the packaging. Insert your new ink cartridges. Close the ink cartridge door.