Pluming questioin

[charles p]

Our washing machine is on a floor above the toilet in my workshop.  When the washer is draining, my toilet starts to bubble.  What is the problem?  Is this air coming back from the septic tank or a venting problem in the plumbing?  How can I correct it?
 
Typo in heading - should say plumbing question.

[blind ear]

You may not have a vent stack where you need it. ear

[FPH]

Do they allow wet vents in your jurisdiction?

[tacklebury]

OR your vent might have a bird nest, dead rat, leaves or any other number of bad things plugging it.  It can be just a few leaves hopefully, but definitely sounds like a vent issue.  If you get it cleaned out, you should wrap the end with some hardware screen double layered and forming and it's good to have a cap over it to keep water damage down some.  If you get a restriction and it fills with water, it will act like a burp valve.