Plumbing and Piping - gurgling pipes

We have a 22 year old house with well-maintained septic (but as old as the house). Our bathroom and laundry room are back to back sharing the same wall. Recently when the washer drains, the toilet gurgles, sometimes actually draining water from the toilet. Once, the toilet was flushed just as the washer drained, and the wash water began coming into the toilet. My husband tried clearing the vents on the roof, but it is still happening. It doesn't do it in the shower or lavatory.

It sounds as though the main line may be clogged, or at least partially clogged. The toilet, with either a 3" or 4" line, IS the main line. The washing machine, with a 2" line, simply dumps a lot of water all at once, and is probably plumbed directly into the main line. The lavy and the shower are also affected, it's just that they are probably farther from the main line, so you don't notice it. Either rent a power snake and clear the main line, or call in a drain cleaning service to do it for you. (My experience, at least where I live, is that one costs about the same as the other.)