after about 2 or 3 minutes of taking a shower in the master bath the toilet starts to gurgle and the shower fills up with water. the 2nd bath also fills up and neither toilet will flush..after anywhere between 30 minutes and 30 hours all the water will suddenly flush out..it is unpredictable, sometimes its fine sometimes its not. my first thought was a venting but the 2 inch pipe appears clear. i have snaked and ran a pressure bladder through the main line and through the shower drain to no avail. i just have to sit and wait for it to drain by itself. the septic tank is also empty. thanks for any help