Cut a 3-inch-diameter hole with a hacksaw in the center of the bottom of a 2- to 5-gallon bucket that has a lid and a handle. Place a coffee filter over the hole, then fill the pot with potting soil.
Hang the bucket by its handle from a hook on a roof eave or other location where the final basket will hang. Carefully cut a slit in the coffee filter and insert the root ball of a tomato-plant seedling through the hole and into the soil.
Drill a 2-inch hole in the bucket's lid, then place the lid on the bucket. Water the tomato plant through the hole in the lid.