So here is my issue. I live in a two story home with 3 toilets. Two upstairs and one ground level. No basement. The two upstairs when flushed and the water empties makes a gurgle sound. The one on the first level doesnt. Here is what ive done so far. I sealed all drains minus the 3 toilets with duct tape. I then plunged all 3 toilets about 15-20 times. I also got some liquid at home depot for drains and put it down both showers in the bathrooms upstairs. kitchen sink, and the washer drain. Water to sinks and showers flow fine and no gurgling heard. Ive read that it can be a clog, air pipe on roof and finally the worst which is a sewer outside line cracked. Anyone have any ideas? could it be the flushing piece inside the toilet where handle flushes? Thanks in advance.