When One Flush Makes Several Toilets Gurgle: What That Sound Really Means

https://yenkee-wiki.win/index.php/Everyone_Hears_the_Gurgle_and_Shrugs_-_What_Water_Hammer_from_Closed_Valves_Really_Reveals

You hear the toilet in the hallway gurgle right after someone flushes the upstairs bathroom. It is not a charming quirk of old plumbing. That weird chorus of gurgles, bubbles and slow-draining sinks is a symptom