We first noticed the problem in the kitchen that when the washing machine (clothes) was running that the kitchen sink would back up relatively quickly after running it to do dishes etc. The kitchen sink would slowly drain, and occasionally a big bubble would rise and it would drain quickly. After that, the kitchen sink would back up without the use of other water sources in the house. We called in a plumber who thought that there was a block somewhere in the pipe. He snaked the kitchen drain with a 75 foot snake and it seemed like the problem went away. At this point I will mention that the under the kitchen sink cabinet, there is an air admittance valve. The plumber said that ours was broken and that we needed a new one, but it didn't seem like he was concerned about it. My landlord decided that he wasn't either and we haven't replaced it. In the past few days, when a large amount of water is to be drained (shower, toilet, washing machine, etc.) the downstairs sinks/toilets will gurgle and eventually start filling up with water. Yesterday, the landlord was over trying to DIY without having to call another plumber and remembered the air admittance valve. At the moment, the kitchen sink was backed up with about an inch or two of standing water. He unscrewed the AAV and the water started draining really nicely. We turned on the faucet and let it run, turned on the tub faucet and let it run and everything seemed good. He's gonna run to the store and grab a new AAV and hopefully that solves things. So I have two questions 1) Could the AAV for the kitchen sink affect the drainage for the other sources in the house (bathroom, washing machine, other sinks etc.)? 2) When the kitchen sink backs up, there are metal filings that settle after the water drains. Could that be from when the plumber snaked the drain? Thanks for you help