When i forget to take them off my pants mostly. I don't wear like nice leather belts though I just throw them in and let them clank around

In the washing machine. Then, I throw them out because they are ruined and buy some more.

I don't actually do this, but I imagine that's what the response will be.

Leather cleaner/conditioner and a brush.

I have a cloth belt. I throw it in the laundry when I go to wash all the pants.

Power washer.

I use saddle soap.

Depends on the material, but with leather I give it a light spray of lysol and then just let it air out. TBH I don't know how effective it is, but I figure it's better than nothing.