Ordinary renovation debris is fine. The restrictions come from Maine state law and from the Saco Transfer Station's own posted refusals, which are more specific than most.
Maine makes it illegal to throw away cathode ray tubes and LCD screens, so old televisions and monitors have to come out of the container. The state also treats business disposal of rechargeable batteries in the trash as illegal, which covers the packs in cordless tools, and some business electronics containing circuit boards or mercury lamps are regulated as hazardous waste outright.
The Saco Transfer Station refuses asbestos in any form, hazardous waste and chemicals of any kind, lead and oil-based paints, gasoline tanks, roofing tar and driveway sealer including their containers, large propane tanks, and appliances containing refrigerant. Car batteries are not accepted either: lithium-ion is the only battery type the site takes, and the rest go to collection points in Arundel or Portland.
Two Saco-specific rules are worth knowing. Japanese knotweed is refused outright, and the City points you to a certified removal company instead, so invasive growth from a lot clearing cannot ride along in the container. And the site does not accept material from other towns, which is one more reason to tell us where the job actually is.
Found something you cannot place? Describe it to your account manager before it goes in the container.