omegared,
I also would select design "A".
However, I bring the INLET water from the pond in from the side of the barrel near the bottom (just below the filter media support platform). This elliminates having to cut holes through the filter media for the pipe coming down through the center from the top (if you are using something like Matala sheet or roll media).
Also, if you have to remove the media for cleaning, the inlet pipe will not be in your way. That is one less step to contend with during maintenance.
If you are using a media bed of rock/gravel/sand, then this configuration will allow for better purging using compressed air and water from the bottom upwards. For either media type, you will provide that much additional filtration (the pipe going down the center takes up useable filtration area).
Having the inlet pipe come down the center of the media from the top also allows for possible channeling of dirty pond water around the sides of the inlet pipe between the pipe and the filter media.
I bring the inlet pipe into the barrel and then TEE it off near the center of the barrel. On each side of the TEE I inserted a short length of pipe with a 90 degree ELL at each end, near the outside wall of the barrel. Each ELL directs the water into a circular flow around the inside perimeter of the barrel. Thus attempting to form a sort of 'vortex' or whirlpool movement of the water at the bottom of the barrel. This action creates a fast current of water around the outer perimeter of the barrel and a 'slow' velocity point at the very center of the barrel. The larger, heavier solids should drop out nearer to the very center and bottom of the barrel.
Then, for the drain, I used a simple PVC shower drain installed at the very center of the barrel, flush with the bottom. Most of the big, heavy "gunk" gets expelled when I open the drain valve.
If you intend to use this filter for merely filtering out solids, then you can apply the cleaning / purging methods below.
If you are using this system as a biological conversion system, then you need to ensure that you don't harm your bacteria during the cleaning / purging process and will have to be more gentle.
If you use Matala type media, I would flush the system from the top down to clean it often (weekly/monthly/qrtly) and drain the wastewater out the bottom. Then, periodically, remove the media from the barrel and clean it with a pressure washer or garden hose sprayer.
If you are using rock/gravel/sand for your filter media, I would use a high pressure air compressor with water assist to flush the media up from the bottom and overflow out to a top drain line (in conjunction with the bottom drain for the barrel).
These are just the ideas that I have incorporated so far, not that they are the best practice or the most most efficient, they were just the simplest for me to design around and make the system more maintenance friendly for me.
Catfishnut
