My pond is only 300 gallons plus a 35 gallon trash can uplift filter. I have 2" pipe gravity flow from the bottom drain which goes all the way to a bubbler drain at the street but along the way it has two vertical risers and a valve after each riser. First riser goes into a 3 gallon bucket that sits just below the water level but 25 feet away so it is always full of water and contains my 1500gph pump. The pump pushes the water through a 1" hose into the lower side of the trash can. The second vertical riser goes into the center bottom of the trash can as well. The drain pipe serves as a sort of heavy debris sump which holds it all until drain time. The trash can has a space at the bottom for my air cleaning apparatus, then a layer of medium gravel, a layer of lava rock, a layer of pot scrubbies, a layer of green scrub pads and finally a layer of ceramic bio rings. Water filters through these as it rises and finally exits at the top through another 2" gravity pipe whose output into the pond is about an inch lower than the bulkhead at the trashcan so it still gravity flows even though all the pipe in between is burried underground. I am new to this whole idea but it seems to be working ok.
The pic of the fish below is a little blurry cause I was moving to track the fish but the rocks seen are 2' down.
I have had no confirmation or input from anyone whether my setup is any good.
Short answer, make sure the pipe exiting the barrel is larger than the pumped intake pipe.
