building a 55 gal biological filter

pic 1 find a clean 55 gal drum ,drill holes in lid then cut it out.......................pic 2 there are only 3 parts you have a water tower, a cut up bucket, and your lid for a grate....................... pic 3 shows the parts together..................... pic 4 shows parts in drum ready pic 5 go ahead and put in filter mat ,fill to top

DrCase

pic 6 shows a one drum set up , go in the top, send the water to the bottom and water filters on the way back up...............pic 7 this is what i am doing adding a second drum tie the 2 together........................pic 8 come out of the first tank connect with tee to send water down to bottom of drum...............pic 9 show 2 drums together and return to pond, the vents keep the system from air locking.................pic 10 starting up 2 nd filter

pic 11 shows the 2 filters as they are now .................. pic 12 shows a rubber cap on the dump valve ,i use this during the winter ,to save my ball valves from freezing . i will no hub a valve on when i get it..........

A PVC Ball Valve works great for the dump.

Are the vents the pipe in the back of the drums that I see sticking up?
Lolly

yes they are vents....my filters are away from my pond...i gravity feed back to my waterfall ,but i go down out of the filter,and back up at the waterfall, to hide the pipes...my filters are about 2" higher than the water fall....the vents keep it from air locking

where are they connected? at the bottom or in line?

i have 3 vents on my filter...i am all gravity return to ponds....i have one vent at my water fall, pic not shown....

Thanks for the pictures that helps alot. It looks like they are in the return line to the pond am I seeing it correctly?

yes you are correct only in the return