I have a bad odor from my pipes in the bathroom from septic tank!

need to call a plumber to fix this. gas fumes from septic are noxious and will make you ill.

Is the tank overflowing? If everybody showers one after the other or takes baths and does laundry at the same time, it is overloading the system at once. If that's not the case, then it is not normal.

When we first bought our cottage we didn't know any better, and everyone ran water at the same time, and we had a rainy summer. Once you get used to it, you know not to do laundry, the dw and a bath at the same time. It was a learning curve for us.

Does it only smell in the bathroom. Ours does briefly if we fill the tub to the top and let the water out quickly, but the tank doesn't overflow. We have no smell with showers. You can put a box of baking soda down the drain or toilet once a month.

Maybe you have a leaky pipe or toilet.

I'm surprised your municipality didn't make you change your system when you built. We don't have a choice here. Maybe something was damaged during construction. If the builder won't do anything, get an inspection done. Septic systems aren't cheap to replace.

Here's a good article:

https://inspectapedia.com/septic/Septic_Odor_Cures.php

Have it pumped out, and if you are still using the septic system, you need to put enzymes down it monthly to keep it functioning properly. I use Roebic products I get at the home store or hardware store.

P.S. Don't put food, grease or strong chemicals down the drain. Even too much bar soap isn't the best. We use mainly bodywashes and liquid hand soap. Aome people put kefir or buttermilk every couple of months...I have never tried it.

http://www.kingcounty.gov/depts/health/environmental-health/piping/onsite-sewage-systems/maintenance/dos-and-donts.aspx