Most household and building debris is fine to load. The limits come from Wisconsin's own disposal law and from what the receiving facility will take.
Wisconsin bans a long list of materials from landfills and incinerators, and the ban applies to homes, businesses and job sites alike. Electronics, lead acid batteries, major appliances, used oil filters, waste oil and waste tires all have to be kept out. So do everyday recyclables: cardboard, glass containers, newspaper, office paper, aluminum and steel cans, and plastic bottles and jugs. Yard waste is also barred, and grass, leaves, garden debris and brush under six inches thick have to go to a compost site instead.
Hazardous waste, liquids, paint, solvents, fuel and asbestos stay out of any standard container, in Milwaukee and everywhere else. Milwaukee County residents have a household hazardous waste program run by the Milwaukee Metropolitan Sewerage District for those materials.
A few construction materials are also treated separately here. The City's own drop-off sites turn away burnt debris, painted brick and block, painted concrete, asphalt, and concrete with iron rods still in it, so plan a different route for any of those.
Got an item you're unsure about? Ask your account manager before it goes over the rail.