Sometimes when I flush my toilet at the cottage it almost overflows and then drains slowly and at other times it works fine. I checked the roof vent and it is clear. I replaced the toilet with an American Standard Cadet 3 and there is still a problem. I am on a septic and it was pumped recently. The person who pumped it said it was full of roots and he cut off as much as he could . It is a 40 year old concrete tank and there is no opening at each end to check the inlet and outlet . When it was pumped though I was told that it appeared to be draining into the field properly. I checked the clean out where the drain pipe goes through the concrete wall and after the toilet is flushed the water does not drain back from the septic tank. The pipe from the toilet to the wall is clear. One time when I flushed the toilet I heard a gurgling sound in the kitchen sink and the shower which are all on the same floor however this has not happened again. The plumbing is all new and was done 5 years ago . The problem just started about a month ago. I would appreciate your thoughts on this puzzling situation. Thanks

I would suggest pulling the toilet and running a large sewer snake down and out to the septic tank. Have somebody stand at the tank and listen for the snake so you know when you have hit the inlet baffle of the tank. If the pumper found roots in the tank, odds are there are roots in the pipe leading to the tank. Augering the drain from the house to the tank would be the best place to start, in my opinion.

I'd go out to the tank but would first look for a clean out opening right where the pipe exits the building

There's a small hole in the bowl. This is the jet that starts the siphon action. Take your finger and feel in the hole. If there's mineral buildup then scrape and clear the jet hole. Let me know if that worked for you. Tom