Looking for advice for venting problem. Since this is my 1st post I'm not sure if I can attach a picture for viewing. Hopefully my description will suffice if I can't. Everything down there is PVC. Vent through roof and toilet drain is clear. No flushing or draining problems with toilet or shower or anywhere in house. Toilet flushing causing gurbling sounds in shower drain and over time empties the shower trap. Shower drain (2") connection is directly below the toilet flange connection then drainage drops down to 3" elbow. Approx 30" downstream of the elbow there's a wye connection which is a vent going up through the roof. After doing some research I see where the "critical distance" for the fixture/vent should be 5 ft maximum. House is about 22 years old and the shower does not have a separate vent so I'm guessing Mr. Inspector might have missed this one. The old low flow toilet worked just fine and never cause gurgling or trap emptying characteristics. I'm not real excited or interested in installing an AAV (if permissible) since it's down in the crawlspace and I'd like to do the job without ever having to visit the area again. I'm considering installing a wye in the 2" shower drain approximately 2 ft after the trap, rolled up at least 45 degrees (outlet of wye facing trap?). I'll need to use a 90 elbow go through 1 joist, another 90 and I'd probably have maybe 4 feet of 1 1/2" pipe running horizontally then go up (another 90) through a wall and connect it in the attic before it goes through the roof. Any problems with the horizontal vent run? Regular 90's OK? Any other issues I should be concerned with?