What you're probably seeing right now
You've got a slow tub, maybe a gurgling toilet, and a bottle of something from the hardware store on Highway 160 that promises to clear it all out. You pour it down the kitchen sink or the bathroom drain, wait the twenty minutes the label says, run some water, and the house still backs up somewhere else. Maybe the basement floor drain starts smelling or the washing machine standpipe burps when the dishwasher runs. That pattern, one product, one fixture, no real change anywhere else in the house, is usually the first clue that the problem isn't where you poured it.
Why one fixture can't talk to the whole system
Every drain in a Nixa house, whether it's a 1970s ranch off Main Street or a newer build out toward Spokane Road, ties into one main line that eventually leaves the house and connects to the city sewer or a septic tank. A bottle poured into a bathroom sink travels a few feet of pipe before it hits a trap, then crawls through branch lines at a slow trickle. It simply does not have the volume or the push to travel fifty or eighty feet through a four-inch main, especially if that main has a belly in it, roots in it, or standing water already sitting in it.
Gravity-fed drain systems depend on slope and unobstructed flow. If the clog or blockage is actually in the main line, not in the branch under the sink, the chemical never reaches it in any useful concentration. It gets diluted, it cools, it just sits in the trap and does nothing. People then pour more down, which mostly just adds a caustic liquid to standing water in a pipe, which is its own hazard if a plumber later has to open that line by hand.
More on this from drain and sewer backup nixa for Nixa homes.
What the Ozarks clay and seasons do to home sewer lines
Nixa sits on the kind of shifting clay soil common across this part of the Ozarks, and clay does not stay still. It swells after wet spring stretches and the heavy thunderstorms that roll through Christian County, then shrinks and cracks during the dry pull of late summer. Older clay or cast iron sewer laterals, common in homes built before the 1990s around the older parts of town, don't flex well with that movement. Joints separate slightly, roots from mature trees along yards and easements find the moisture and work their way in, and over years that produces a partial blockage well outside the house, often under the yard or near the street.
Winter brings its own version of the problem. A hard freeze can tighten already-settled soil around a line and briefly worsen a partial clog that was manageable the rest of the year. None of that is something a fixture-poured product can reach, because the blockage isn't near any fixture at all.
What you can actually check yourself
Start by figuring out whether one fixture is slow or whether several are acting up at once. If only the upstairs bathroom sink drains slow, that's a localized issue and a drain snake or plunger at that fixture is reasonable to try. If the tub backs up when you flush the toilet, or the basement drain burps when the washer empties, that's a main line symptom, not a single fixture problem.
Check your cleanout if you have one, usually a capped pipe near the foundation or in the yard between the house and the street. Standing water near that cap, or water that rises when you run a fixture, tells you the blockage is downstream in the main, not up in a branch line. You can also watch for sewer smell in the yard or a soggy patch over the lateral line, especially after rain, which points to a line that's already cracked or separated underground.
When it's time to call someone
If more than one fixture is affected, if the cleanout shows standing water, or if the backup keeps returning every few weeks no matter what you pour down a drain, the problem is in the main line and needs a camera inspection or a proper auger run from the cleanout or roof vent, not another bottle from the shelf. That's especially true in homes with older clay or cast iron laterals, where root intrusion or a settled joint needs mechanical clearing and sometimes a line repair, not a chemical.
Repeated caustic treatments can also damage older pipe from the inside, which turns a clog into a cracked line. At that point you're looking at excavation, which is a bigger job than anyone wants to discover by accident. If you've checked the cleanout, ruled out a single-fixture clog, and the backup keeps coming back, that's the point to stop troubleshooting and get a professional look at the actual main line.