Filter housing I designed because I drink a disgusting amount of water, and I didn't feel like paying PUR any more money for charcoal encased in plastic.
If you too want to make your own filter, I recommend printing the final product in PETG, as it's a food safe plastic.
Keep the sealing o-ring on your spent filter and use it with this one. Depending on how fancy your printer is, the threads might not seal perfectly let a trickle of water through. If this is the case, use something to seal the threads. Silicone, petroleum jelly, etc.
As for as filling the actual filter, that's up to you. I've used a filter pad on the top and bottom, with granular activated charcoal (20X50 mesh) with great success.
An example of some good activated charcoal to use: https://www.highwaterfilters.com/products/1-lb-granular-activated-carbon-20x50?_pos=5&_sid=c4bf38868&_ss=r