My mother lives in a two bedroom trailer with two full bathrooms. It's got a septic tank, but the toilets bubble and back up anytime she uses the dishwasher, washing machine or runs water in the sinks or tubs. Worse, sewage backs up into the tubs and over fills the toilets. What could cause this? Could it be a blocked air vent for the plumbing, a clogged pipe, or a septic problem?
Simple answer: yes, it could be any and all of those. In my experience, clogged main pipes is the most likely cause. (See below for more detail.) If you cannot use a motorized snake yourself to clean out the system, hire a professional. There is also a chance the septic system needs to be serviced.
Hire a professional plumber who can use a motorized drain snake ASAP. We had a similar issue, neglected it for a year, and during a visit from the in-law, the toilet decided it was done and overflowed. The HVAC system was also a victim (in-floor registers). By waiting until two days after the overflow, we saved a few hundred dollars over an emergency call, but we could have saved more by addressing it quickly.
The individual who does the "snaking" should be able to snake the entire system, from all clean-out locations (our system had multiple). Also, if the system has vents which can be compromised (squirrels or other pests with nuts etc.), consider having those cleaned if the price isn't prohibitive. The company who provided the service to us charged by the hour a much reduced rate after the first hour had elapsed. If we had the option, I would have preferred this. (In our case, the service personnel had two more calls to make after finishing our property after 5 pm. I was told that if anything wasn't completely working properly, the servicer would return on their dime, and I wasn't about to keep someone from their family around the holidays.)
I can now say from definitive personal experience: hire a quality professional to minimally snake and clean the system - but preferably have them do an inspection as well. A
Do it right, right away.
You almost certainly have a dead septic field, but start out by having a professional come out and "roto-rooter" i.e. clean out all your drain lines. It's possible that there's tree-root invasion, but given that you're getting sewage backflow, more likely the tank outlet is clogged or that the leaching field is dead. You should take a look at the ground where the field is. Softness or sewage smell there will be an indicator of trouble.
The problem you are seeing could be several different things.
First, the line to the septic tank could be obstructed. This happens with hair, toilet paper, poop, fats, fabric softener, etc. which create gunk which is just a little too think to get encouraged down the pipe. Because the flow is not clear to the septic tank, and because gasses cannot flow back easily to the vents in the trailer/house, one gets bubbles when flushing. Because the water displaces gas in the pipe which has restricted flow.
Cure? Snake the like to the septic tank. If it is just getting restrictive, perhaps a "balloon" may help, where you access the line after the last connection in the trailer, and push the gunk out with pressurized tap water. The balloon expands to seal the end of the pipe you are pushing from.
Second, the tank may need pumping. Depending upon the size of the tank, and the household load (flow of water and solids), tanks fill at varying rates. For one person, probably not a big deal. But with several kids or teenagers, things will fill fast.
Cure? Pump the tank.
Third, the leech field may be clogged with dead bacterial matter and other gunk. This happens most frequently on a system that is being used over capacity, or has gone too long between pumping out.
Cure? Most expensive situation, because the leech field may need replacement, or some kind of remediation. What you can do is often dictated by the state health department, or sometimes the county or other local health department.
Most likely, the line to the septic tank needs clearing. The balloon trick costs about $10, if one already has a garden hose. I would try that first. I would also look around the septic tank for water coming out of the ground, showing that the tank is spilling over. This can happen because the downstream system is not working well.
I would start ruling things out upstream, which is for me the line from the house to the septic tank.