Sewer line blockage

A little history....
I have a 25 yr old 4 bedroom colonial built on a slab. I have a clean out in the rear outside of the house and a vent in the front of the house (2 ft off the ground) that goes into the wall of the garage and then elbows down into the garage slab. On this pipe that goes down, a drain for the water softener goes into the side of it and also a drain for the boiler condensation goes into the side of it. A few years ago I had a problem with the boiler drain freezing there and it backed up into the boiler and causing it not to work right. So I put a tee in the pipe about halfway between the boiler and the pipe junction. I figured if the joint froze again, the water would simply leak out that tee and not cause the boiler to fail starting. No big deal as it's a gallon a day tops in the winter.
Once during the summer, water started pouring out that tee and flooding into the garage. It certainly didn't come from the gas boiler. Happened again today. I have 1 toilet on the bottom slab level and it bubbles when this is happening and will overflow if flushed. Usually happens when someone is taking a shower upstairs I believe
Am I right in assuming that there is a blockage somewhere under ground or below my slab to cause this The line runs to a street sewer line 75 ft out.
What to do???
Thanks

First, here's what you don't do. Don't try to clear the clog with chemicals. They will not work and they will create a hazard for the professional that you end up calling. If you already have used something, tell the plumber what, when, and how much you used so he can protect himself from serious chemical burns. Next thing not to do is try a DIY snake. These are seldom large enough to do the job and frequently will make the clog worse. Professional equipment is dangerous to mess with as well even if you could find it. OK, now you might have already inferred where I'm going with this. Call a plumber that has the professional equipment and skill to properly auger the drain. We usually suggest you avoid companies that have "Rooter" as part of the company name. While some of these may be OK, many do not have the overall skill and equipment to do the job right.

Quote:

---

Originally Posted by Gary Swart

First, here's what you don't do. Don't try to clear the clog with chemicals. They will not work and they will create a hazard for the professional that you end up calling. If you already have used something, tell the plumber what, when, and how much you used so he can protect himself from serious chemical burns. Next thing not to do is try a DIY snake. These are seldom large enough to do the job and frequently will make the clog worse. Professional equipment is dangerous to mess with as well even if you could find it. OK, now you might have already inferred where I'm going with this. Call a plumber that has the professional equipment and skill to properly auger the drain. We usually suggest you avoid companies that have "Rooter" as part of the company name. While some of these may be OK, many do not have the overall skill and equipment to do the job right.

---

I appreciate your advice. I have not treated it with anything. It's only happened a handful of times in the last 6 months. Can't put my finger on why so intermittent. I have no trees anywhere near the line except for the usual shrubbery around the house. What could partially clog the line if it's not a root problem.
The main guys are of course Roto Router (of course) and another called Rooter Man. A few others that describe themselves as family businesses.
Any idea of the cost?
Thanks

It will cost whatever they charge, but it will cost a lot more if you don't take action and the sewer backs up into the house.

What can cause an intermittent blockage? Could be something was flushed that shouldn't have been and get wedged in the pipe. I will collect paper and debris causing the block the crug can wash free and everything seems to work OK for awhile. May not be the only answer. Try a full service plumber for clearing the drain. The franchises are rather "iffy" on qualifications. Some may be really good, but some are hacks. Cost for services is impossible to even guess. Don't know where you are, but labor charges vary widely from place to place. What might cost $100 in one area could cost $500 in another area. In addition, there's no way to tell how long it will take. If you were getting an oil change in your car, price and time could be reasonably estimated, but how long it will take to deal with a clogged drain is another matter all together. As Catcher-Chick said, "It will cost what they charge, but it will cost a lot more if you don't take action and the sewer backs up into the house."