I have something blocking part of my main drain line in the my house. If I run several things at once such as dishwasher and washing machine or a couple of showers at once, the showers get water coming back up into them. It doesn't happen very fast and the water drains out eventually. Is there anything that I can do before calling a plumber? I haven't used a pipe snake before. Some people where I work have said to put muriatic acid down the drain but I have read not to do that on several forums and haven't found an online source that says it is ok to do so.

snake it. It will give you an idea what you're dealing with - tree roots, etc.

I can tell that the clog is under the house portion of it. Water doesn't flow to the clean out that is outside of the house so I do not think it could be tree roots.

Sounds like you may have a break. If it gets down the drain (sink, tub, washer, etc.) it won't clog the main line under the house. I think renting a snake long enough to get where you are going is just money you are going to need later.

We recently had to replace 90% of the plumbing in our house - built in 1962, slab foundation, cast iron pipes that just corroded over time in a couple of spots. Symptoms were similar to what you describe and deteriorated over time (and after many snakings). We were freaking out a bit about jack hammering through large sections of hardwood floor, tile and slab. We are in East Texas and ended up using Bannister Plumbing to re-line the pipe. They just had to dig one hole in the house and one big one outside - then use fancy equipment to grind and clean the existing pipe system, running cameras through the pipes, etc. After old pipes are clean and prepped, another machine is sent through to re-line the existing pipe with some pvc-ish substance. We have been very happy with the result and thrilled that the cosmetic damage was minimal. Just a suggestion to explore if it might work for your situation.

my also just be a sag in the line, effectively narrowing space through which things can flow