cat and litter box

Okay ladies I need your help. My beloved black kitty went missing 2 months ago. I wanted to fill that void so I got a new kitten. He was only 5 wks old when I got him so I had to take him to the litter box myself. He was doing so good! But once he learned how to on his own I stopped taking him. He Started going poop in our plant so we put it outside. Now he's going potty behind our washer and dryer and it's very difficult to get back there and clean. He's 8 weeks old now so what do I do? I keep putting him in the litter box but he still isn't listening. I'm at my wits end with this cat😫 someone please help me. I've never in my life had this problem!