Place duct tape over sides and bottom of the plastic container or bucket. The goal is to prevent light from entering the interior of the container and causing algae to grow. If the container you chose is a dark color and does not allow a lot of light to penetrate the sides or bottom, you can still apply duct tape to prevent what little light there is from penetrating and causing slow algae growth, which will kill the roots of your seedling.
Drill a 1/8-inch hole about 1 inch from the top of the container. The hole should be located in the back portion of the container. Insert the black air hose into the container through the drilled hole and connect the air stone to the black hose on the inside of the container. The air hose can be purchased from any pet store or aquarium supply.
Drill a 1-3/8-inch hole into the lid of the container, place the lid on the container and set a similar sized net pot into this hole. Note where the bottom of the pot rests, as the pot should not reach all the way to the bottom of the plastic container. There should be enough room in the container so that the net pot rests just below the water level. You don't want to have the developing roots saturated, just nice and moist.
Remove the lid from the container and fill with water up to the level just below the net pot. The air stone should be heavy enough to stay submerged, if it is floating you can use some clean stones to weigh it down.
Connect the other end of the black hose to the air pump and plug it in. Look inside the container for the bubbles to make sure the air pump is working. Replace the lid and push down firmly to lock the lid in place.
Insert the seed into the plant growth media. Rock wool or clay pebble medium is one option, but that requires a preparation washing of the dirt and dust particles to get your plant growth media clean. The other option can be found in hydroponics stores and online and resembles a light foam material. One company that developed this type of media is called the Sure to Grow. It is available in different sizes and can be used for seeds or propagating cuttings from existing plants. They call this media the Storm Series or Hail.
Place the plant media into the net pot with the pump running. Wait about seven to 14 days for the roots to begin to develop. At this point you can add a minimal amount of nutrients to the water so that the roots continue to grow. If the seed you are starting is of a larger plant, you will need a support system to allow the plant to continue growing. Which nutrients you add depends on the type of seed you are germinating.
Watch the water level and add more as needed. Keep the level at the same point and make sure the air pump is running constantly, generating the oxygen the plants need to survive.