In January 2010 we started having problems with our toilet not flushing properly. In the early morning it would flush fine, but by about 10 am, when the toilet was flushed, the water level in the bowl would rise very high and then not all of the waste would drain out. When the washing machine drained and sometimes while taking a shower, air would bubble up into the toilet bowl. This sometimes even happened when water was not being used anywhere else in the house. We tried snaking the toilet ourselves, but this did not help. We finally called in a plumber and they used a large snake and came back with a huge clump of hair about 100 feet out in the line. The toilet worked fine again until September 2011, then we started having the same issues again. We called the plumber again and this time when they ran the snake, they did not find anything in the line. However, they said that they thought that the sewer line may have collapsed somewhere near the house and would need to be replaced. We dug up the line and found the area that they indicated, however, it was not a collapsed line, there had been a repair made previously to the spot, replacing the cast iron pipe with PVC. The toilet worked fine for about 3 weeks, but now it is acting up again. It will flush OK, two or three times, after that when it is flushed, either the bowl does not fill to the correct level, or the water rises too high and then does not go back down to the correct level. Usually overnight the water level in the bowl goes back to where it should be. My husband discovered some insulation in the vent pipe that comes out of the side of the house yesterday. Could it be that the clogged vent is causing the problem?