I believe you mean top feed or drip. You have a pump that drips water through spagetti tubing on top of the medium then some hoses in bottom of bucket to get it back to res. could run pump all the time or a few times a day. easy DIY project, just water pump air pump and some tubing and optional pump. an example is the hydrofarm module, it uses an air pump rigged up to a cool little dripper that squirts air in and forces water from bottom of bucket to the top of bucket.
or!
bottom feed or flood and drain. pump on timer feeding BOTTOM of pot to fill up pot then emptys out. Repeats a few times a day This one is nice because it pushes all the old air out as it fills up with water then when it emptys it sucks fresh air in. a little harder to make yourself because you need a controller that wont allow the bucket to overflow..
hope this helps!