I have used a DIY bottle filter about 3 years ago.
It was in my 60L tank and was relatively primitive.
Ordinary 2 Litre bottle - poke holes in it at the bottom, fill with gravel at the bottom to cover the holes. Cut bottle in half and cut lid and screw section off. Then turn top half upside down and push it into bottom half until secure. I overkilled it with the filter wool, which I stuffed down the center. I then put a small powerhead at the top.
However, although it worked as a temporary filter, I had to remove it when the proper filter came. It was annoying especially when my baby fry somehow got sucked into the bottle through the tiny holes. They survived, but it was a job to keep removing all the filter wool/gravel to get them out. (I guess putting some tights round it would keep the fry out)
I wouldn't recommend it long term, but for a temporary filter or a supplementary filter it works just fine.
"Fall in love with some activity and do it! Nobody ever figures out what life is all about, and it doesn't matter. Don't think about what you want to be, but what you want to do. Keep up some kind of a minimum with other things so that society doesn't stop you from doing anything at all.” - Richard P. Feynman