Here is what P&L Roofing and Flashing Sealant looks like for those of you that need a visual:
4) Next, we are going to build a little stand out of 3/4" PVC so that our media can sit on it, and it's above your swirler. Take a close look and buy the fittings seen here and put it together as such. It's just a cross piece in the middle, 4 elbows and some length of 3/4" pvc:
Now, put your little stand in your your filter like this:
5) Now we need to make a little grate for your media to sit on. You can use a lot of different things to do this, but I happened to use a light grid that you can buy at your local home improvement store. You get 'em in the aisle where the drop ceilings are. These panels are sold in a lager rectangle of about 3 feet long and are about $11 each. The downside is that they are brittle, so be careful. I've seen people use dog crate grating and other similar things. You then cut your grid to fit inside the barrel snugly with a pair of snips. This takes some time, so have some patience:
This is what it looks like in the barrel, sitting on top of the little stand we made above:
6) Now it's time to think about your media. Really, truly, the options are vast here. First you will need a layer of mechanical media. This will serve to stop the crap/poop from going higher in the barrel and re-entering your pond. I don't like ponges because I feel that they clog easily. That's just my personal opinion, and you can use them if you're on a tight budget. However, do realize that you will need to get new sponges every year or two. My personal preference is for a product called Matala. It is not cheap, however, it will last you many, many years. So, I consider it an investment. Matala comes in rectangle sheets, and you cut it to fit. I like to use the black and green matala pads, since they are not too dense. These pads are also very easy to clean.
Here is what they look like after I've cut them to fit my barrel: