So, tagging on this thread -
We recently had our septic tank pumped (2 months ago).
When the washing machine is run, the toilet in the hall 1/2 bath on the other side of the house will not flush normally. It will eventually drain, but not "flush".
The tub in the master bedroom will gurgle when that hall bath toilet is flushed - but only if the washing machine is run. Otherwise, there is no gurgling on any drains.
When the washing machine is not running, that hall bath toilet flushes fine.
Other toilets in the house flush just fine.
There are 4 plumbing vents coming through the roof.

Research online points to a vent problem, or a clog in the drain line.
Not helpful. . .

I plan on getting a "watering wand" from Lowes that has an adjustable head to try to put water in the vent lines to try and clear them of any clog. It's a 14/12 pitch roof, so I don't want to get too far up the roof, and a 70" watering wand will help with that.

The house has a crawl space, and I also plan on getting under there to open up some of the cleanouts and see if there is any standing water in there. If that's the case, I wonder if the outlet on the septic tank may be partially plugged.

Anyone have any ideas?