When I first noticed the problem, it was just the gurgling downstairs when my wife was in the shower upstairs - she likes to use a large shower head and handheld shower at the same time - lots of water flow. It got my attention, and I started reading up on it - this was maybe Thursday night. The next day it gurgled during my shower (I use a low flow head - and long showers), and then later overflowed when she took her shower. On Saturday I had her watch while I took a shower and yell if there was a problem - I hadn't been in that long when she yelled. She managed it with a carpet cleaner. I found out this morning that I can do a quick shower - on and soap - then on again for rinse. The fact that it will eventually overflow leads me away from the vent and more to the drain and septic system. So not completely blocked, but definitely slow to drain. So far the front loading washer and dishwasher do OK, but we're limiting that to real necessities. It's a nuisance, but better than when the power goes out - and a lot better than the snowstorm when we lost power and water.