My down stairs bathtub will fill up with soapy water while I am doing laundry in my laundry room that backs onto th bathroom.The bath tub always drains real slow,I am wondering if I have a venting problem and how to check it?

Hi Steve,

This sounds more like a partial clog in the drain line rather then a vent problem. The solution is to snake out the drain from the lavatory roof vent.
Put out enough cable to reach the base and about 20 feet more. If the tub still drains slow then click on back. Good luck, Tom