I did not notice that some buildings would generate waste without demanding a product. I have to check is town buildings can generate cargo without being supplied by something. I'll be back...

EDIT: town buildings seem not to be able to spontaneously produce products. That seems an attribute reserved for industries. So, I modified the distribution of waste and mail producers so that only the town buildings that demand products can produce products. Next update of Senseless V2 will have this modification.

FYI:
A random screenshot of the residential buildings outputs:
https://i.imgur.com/q4Ybhdw.jpg

I saw it, indeed. The icons suggest that the building will produce waste, but technically they can't (not implemented by the developers). So there is no waste appearing at the cargo stations. Next update buildings will not show production icons alone. The town buildings with production capabilities will always need an input.