My situation is kind of hard to explain, but I'll do my best to give as many details as possible....
We bought this house 8 months ago. The house was built around 1960. The main part of the house is on pier and beam, and it has a large add-on that is on a slab in the back of the house. There is one bathroom in the main part of the house with the original cast iron tub. The add-on has a bathroom with a shower. I don't have any idea when the add-on was built. Guess I should have asked the seller. lol
Anyway, when we first moved in the house, we noticed that the tub drained slowly. I tried plunging it, and then running a snake down the drain and overflow. It would start to drain a little faster after plunging it, but it never has drained very fast. We also noticed that the toilet in the add-on would back up if there was any water running in any other part of the house, especially the sink right beside the toilet. Plunging the toilet didn't seem to do any good at all, and if left alone, the water would go down on it's own after a couple of minutes. After a couple of months of living here, I noticed that when water was running in any part of the house, the toilet in the add-on would bubble. The next thing that happened was a couple of months later. I was taking a shower, and looked down to see that I was standing in a couple of inches of water. It was the only time that the shower backed up while I was using it. Nothing happened again for a little while except for the bubbling toilet until about a month ago. My wife took a bath at about the time that I was getting ready for work. I went into the add-on's bathroom, and was hit by a horrible smell, but couldn't find the source. When I got off of work the next morning, I went to take a shower and the shower floor had toilet paper and other bits of sewage on it. It was cleaned out, but when my wife took a bath again that day, sewage came up from the shower drain when the tub was drained. We cleaned it out, but every time that the tub was filled and drained, the shower would fill with sewage. Earlier this week, the sewage came back up, and spilled over the lip of the shower and out onto the floor. We called Roto-Rooter out. He ran a drain snake through our main vent (we have one for each bathroom). When he was done, we tried to get the shower to back up, and we couldn't, but the toilet in the add-on still wouldn't flush right and the tub still drained slow. He tried to run a camera down our vent, but the camera wasn't working. He told me to go back into the house and flush both toilets at the same time. We did, and when I re-joined him on the roof, I asked him what he thought was going on. He said that we had a sag in our sewer line somewhere under the slab of the add-on.
After reading online about some of the "rooter" companies' practices, I've decided to get some other opinions. I can't afford to hire another plumber right now, but the issue does need to be fixed, and knowing what I'm dealing with will help me prevent any more disasters until we can fix the problem. Any help or questions would be very much appreciated.
I forgot to mention that the Roto Rooter guy told me that the tub drains slow because he thinks that it has a drum trap. He explained what it was (I'm a novice when it comes to plumbing), and it seemed to make sense, to a degree. I may just be thinking about it wrong, but I don't see why a drum trap would make the tub start to drain a little faster after being plunged. Maybe there's just something about it that I'm ignorant of. Anyway, thanks in advance for any information I can get. If anyone wants to know more that I neglected to tell, please ask.