Bio , Green Plastic Toy Soldiers, or Plastic Bath Scrubbies for Wet Dry Filter Media?

I just bought a used 75G acrylic tank with a built in wet/dry system, but it didn't come with anything but the tank! I know wet/dry provides great filtration. I am doing a planted freshwater tank and I also know I should add a mechanical filter to pull out debris and decaying plant material, polish, etc,... but what do I put in all those mysterious chambers in this wet/dry system? I ume some sort of sponge material should go someplace, then I need what? Bio ? I heard green plastic toy soldiers work well, but I think that must be just a charming aquaria myth. The man I bought the tank from said he just used plastic bath scrubbies from the dollar store. I am no stranger to aquaria. I have had tanks for over 30 years. But this is my first time at bat with wet/dry and it is on a tank with some crazy compartments on the back and it came with no instructions. Once I buy a pump and watch it go I'm sure I will figure it out. But I am wondering what media works best for you? And if you have any leads on instructions for a 75 g with a built in w/d filter, please hit me up. I have looked. I came up with squat. Thank you for your time.