I noticed that negations are often made without articles in Spanish. This way, no number is emphasized: these houses may have had "a drain" (one drain) or separate drains for every house, but the fact is that they just don't have any drains. This is my understanding.
Since "gue" or "gui" usually make the noise "ghe" or "ghee" (similar to que and qui), the ü means that the u sound is explicitly pronounced. e.g. "pingüino", penguin, pronounced "pin-gween-o." Hence "desagüe" is similarly pronunced "des-a-gway".