Have you checked if there's a floor drain trap that's dried out? Sometimes a dry trap can let sewer gases back up and cause weird drainage issues. Also curious—when it backs up, is it after heavy rain or just randomly? Had a similar issue once and turned out the city sewer line was overloaded during storms...took forever to figure that one out. Might be worth seeing if neighbors have similar issues too, just to rule out bigger problems.
Dry traps can be an issue, sure, but honestly, if it's backing up repeatedly, I'd lean toward tree roots invading your sewer line. Had that happen here—roots love moisture and nutrients, and they can cause intermittent backups even without heavy rain. Worth checking into...
Had a similar issue here last summer—thought it was roots too, but turned out to be a combo of grease buildup and some random debris (kids flushing mystery items, anyone?). Roots are definitely a common culprit, but before you go digging up your yard, might be worth having someone run a camera down there. Saved us from unnecessary excavation and kept my garden intact...mostly. Good luck!
Definitely second the camera inspection idea. Had a similar headache a couple years back, and I initially suspected roots too. Turned out it was mostly grease and soap scum buildup—who knew those "eco-friendly" soaps could still cause trouble? Anyway, here's what worked for me:
First, I had the plumber run a camera to pinpoint the exact blockage. It wasn't cheap, but it saved me from tearing up half my yard unnecessarily. After that, we did a hydro jetting session to clear out the gunk. Worked wonders, and my basement drain has behaved ever since.
Also, if you're into DIY prevention (like me), consider installing drain strainers and regularly flushing hot water mixed with baking soda and vinegar down your drains. It's gentle on your pipes, eco-friendly, and helps keep buildup at bay.
Hope you sort it out soon... basement backups are no fun at all.
Did you notice if your plumber mentioned anything about pipe slope or pitch during the camera inspection? I've seen a couple situations where the drain line itself wasn't angled properly, causing repeated backups even after clearing out the blockage. Sometimes grease and soap buildup is just a symptom of a bigger issue like improper drainage. Hydro jetting is great for clearing gunk, but if the pipe slope isn't right, it might come back again sooner than you'd like.
Also, curious—did you switch away from those eco-friendly soaps after your experience? I've been wondering myself if switching products really makes a noticeable difference in preventing buildup...