Set one storage tub right-side up on a flat surface with a pond basket next to it.
Mark the height of the basket on each side of the tub. Use a ruler to connect the marks so you have a straight line all the way around the tub.
Cut along the line with a handsaw or jigsaw. Try to make your cut as straight as possible so the tub will be level when it sits upside-down in the second tub.
Turn the bottom portion of the cut storage tub open-side down with the pond basket upside-down and centered on top of it.
Trace a circle around the rim of the basket with a pen or pencil.
Cut a hole in the tub with a razor knife, using the circle for reference, but keep your cut about 1/2 inch inside the circle. This leaves you with a hole just smaller than the opening of the pond basket.
Drill four 1/8-inch holes around the large hole you just cut, about 1/2 inch from its edge. These will allow you to insert zip ties to fasten the pond basket to the tub.
Cut a hole in one corner or along one edge of the tub just big enough for the PVC pipe to fit through.
Drill 1/8-inch holes all over the remainder of the cut tub's bottom. These will act as aeration holes.
Mark the height of the pond basket on the side of the second tub. This will let you know where to drill the overflow hole later.
Set the pond basket right side up on a flat surface and place the cut tub open side down over it.
Attach the basket to the tub with zip ties inserted through the holes you made for this purpose.
Put the pond basket and cut tub into the bottom of the second tub so you have a screened platform. The area underneath will be the reservoir for your self-watering container.
Drill a 1/2-inch hole through both tubs about 1/4 inch below the mark you made on the outside tub.
Hold the PVC pipe upright next to the outer tub and mark the height of the overflow hole.
Drill four or five 1/8-inch holes in the pipe below the mark you just made.
Insert the pipe, drilled end down, into the hole you made for it in the corner of the inner tub. This is your fill tube; the holes at the bottom will allow water to flow into the reservoir.
Place your new self-watering container in its permanent location.
Add moistened potting mix to the container, filling the pond basket first. Add just enough mix to cover the platform.
Fill the reservoir through the PVC pipe until water comes out of the overflow hole. The soil in the pond basket will stay in constant contact with the water, wicking it up through the soil in the rest of the container to keep it moist and your plants watered.
Fill the rest of the container with moist potting mix, patting it down gently as you go. You're now ready to add plants to your self-watering garden.