I am on septic tank out here in the country. I am not sure what the clean out is? I had new tail lines put on the septic a few years ago. The house was built in 1961 and had terra cotta which had pretty much collasped.. This was replaced with some type of PVC which goes across the property about 200 ft. Backhoe came in and did the work and it is about 4 - 5 ft deep best I could tell. As far as I can tell I don't have a problem with drainage.
Now...with that said I will have my husband try going in through the other vent and tub overflow. There is no problem with roots etc. in the lines. We have replaced some outgoing lines under the house but the 4 inch line going to the septic is cast iron. He has some type of pipe he pushes through the 4 inch to the septic wall and that helps for a while. It is always clogged or blocked when he works on it. OK guys this wife appreciates all the help you are giving us. I look forward to the replies!