Sewer problem question
We live in a two story house with basement, house approx 30' x 25 so not a large footprint. Am have a sewer gurgling problem which have been told it's probably roots in the outlet pipe that connects to the main sewer line.
There is an approx 3" dia vertical pvc pipe in the basement washroom that is approx 14" in depth with a cap on the top. Anytime when everything is working correctly there is approx 1" of water at the bottom. Three items discharge into this, the toilet, sink and shower.
My question is that now with this gurgling action and slow flush of the basement toilet this level is now at approx 4" below the top of the cap. So approx 10" of standing water and it doesn't matter how much water you pour down this pipe from the toilet to the shower this level doesn't change. Flushing the toilet creates bubbling and a slight increase in height for a few seconds but doesn't overflow and returns the this 4" height.
How can this be, if blocked it would continue to rise each time I flush the toilet. I am suggesting there is a blockage of some sort and understand water finds it's own level but this water is going somewhere.
Any suggestions please, many thanks for any help,