Step 1: Supplies
Old inflatable ball. I used a worn out size 5 soccer ball that still holds air, which is important.
Exacto-knife or other sharp blade to open a part of the seam and pierce the inner rubber bladder of the ball.
Funnel- for adding the sand.
Basin- to steady the ball and catch any sand that spills.
Bicycle tube patch kit, or rubber cement and an old inner tube will do the trick- to seal the hole in the bladder
Duct Tape- for closing up the cuts. You could resew the ball, but mine was so worn out, this was really the only way to go.
Air pump- for inflating the ball and making fart noises with you belly button.
Step 2: The First Incision
Making sure you only cut the laces, carefully start to cut through a line of them. You want to pick a small panel that can be put back together easily and not show that you've been operating on it. Do not cut out the entire panel. One or two sides and maybe part of an adjacent panel should be enough to get into it.
In this ball and probably most others, the inner bladder adheres to the outer skin, so it's really close to wear you're cutting. It separates easily simply by pushing it with your fingers. If you do cut all the way through, though, and hear the rush of air coming out, don't worry, this will become your bladder hole in the next step.
Step 3: Pierce the Membrane
Step 4: Sand Transplant
Insert the funnel into your slit and place the ball in the corner of the basin. This will stabilize the ball as you pour and catches any that may spill out.
Fill 'er up or add your pre-measured weight.
Step 5: Start Closing
Rough up the surface
Size and cut a patch
Apply glue to patch and bladder surface, making sure you cover the entire area.
Allow to air dry for 1-2 minutes before affixing patch to bladder.
Work out any air bubble that may be around.
At this stage I put a little air into the ball so I had something to push against. Not much, mind you, you don't want to blow out your patch before it sets.