Okay then: what's a cold upflow filter?
A cold upflow takes dirty "wet" VO and introduces it to the bottom of a drum via a tube attached at the top of the drum. The dirty oil, heavy with contaiminates stays on the bottom while the clean oil floats to the top. Particulates and water like to cling together, so the bottom gets dirtier and dirtier and as the contaminates clump it frees clean oil which is lighter and it floats up.
Here is how mine is assembled.
I have a 55 gallon drum on a 18" tall stand. Threaded into the 2" bung is a 4" long nipple with a pipe welded to the inside of the nipple. Once the nipple is threaded into the drum with the pipe on the inside, the pipe is about 6" from the bottom. On the other end of the nipple I threaded the top 1/3 of a 55 gallon drum to act like a large funnel. Inside the "funnel" is my 75 micron screen.
As I pour oil into the funnel it gets filter to 75 micron and enters the pipe and begins to fill the barrel. The 3/4" bung has a PVC elbow and is pipe to my WHWF (whole house water filter) and then into the next barrel. As the 1st drum fills, it pushes air out of the 3/4" bung until the drum is completely filled. At that point you stop adding oil for atleast 1 week.
After 1 week the oil should have settle fairly well, with the cleanest, driest oil on the top and as you add say 5 gallons of "dirty" oil, it is piped straight to the bottom and pushes the entire column of oil in the drum up, pushing 5 gallons of clean/dry out. The WHWF element creates resistance to the flow and keeps the flow slow. The slower the better as it gives the "junk" in the bottom oil that is getting pushed up time to settle to the very bottom. This will not only separate out food particle/sediment but it will also separate out fats and partially hydrogenated oil (PHO).
I have processed as much as 10 gallons in a 24 hour period, but don't recommend going faster than that as you may start to push dirty out out. The warmer the oil temp the faster the junk will settle out and the whole system stops once the temp drops below about 40F. I have installed a drain at the very bottom to drain out all of the sludge once a year.
This system works very well, but it does work slow so you will need to build up a supply of clean oil before you need it. And unless you build a warm upflow, like I said, it will "freeze" up in the winter. However, once your oil is clean and dry it will stay liquid below 0F. I know this because I pumped clean oil with a drill pump at -5F last winter.
I have at this moment a 275 gallon tote filled with clean dry WVO. I hope to process and fill 2 more 55 gallon drums by freeze up and that will get me through the winter. I still collect during the winter, I just have to wait for spring to start processing again.