If a pillow case is all you can get, it’s all you can get. But use an old one, preferably an old white one. And brew small batches. Start with light beers that have less grain per water.I can't get a brewing bag, cheese cloth or paint strainer in my town, can I use pillow casing? On a pillow casing the holes are way thinner than a brewing bag, how will that affect the wort?
If there is any way to get one with larger holes.
What about trying to use a smaller pot that just slides into your bigger pot. Drill some drainage holes and line the bottom with mesh, course cloth layers etc
How did brewers drain their wort before bags were invented? A lid that slips down into your pot to hold back grains? Then just ferment the cloudy wort?it doesn’t have to be perfect, just keep out most of the sludge