When septic systems begin to fail, your waste will start to seep into the groundwater. You may notice a foul odor (it’ll smell like sewage) or a squishy, moist lawn. The grass right over your tank or drain field might grow super lush and green because your waste actually fertilizes it. Other signs include standing water in your drain field, slow-draining sinks and tubs, and gurgling noises in the plumbing.

When a septic tank is full, it needs to be professionally pumped. The average cost of a one-time septic tank pump is about $400, or $0.30 per gallon. If your septic tank is full, you may notice that you have issues flushing your toilet, pipes are draining very slowly, or you have a sewage smell lingering in your home or yard.

A gurgling toilet usually doesn’t mean that your septic tank is full. If waste can’t drain into a full septic tank, you’ll see water and sewage backing up into your fixtures, but the air that causes gurgling is a result of poor venting. You are more likely to have a clog in your vent stack or a damaged air admittance valve.

It is generally safe to stay in a house that smells like sewage for a short time, but you should get the problem fixed as soon as possible. While the level of sewer gas is usually low enough to only cause minor symptoms, prolonged inhalation can lead to headaches, nausea, or respiratory irritation. High levels of gas exposure can be more dangerous, and high concentrations of methane—a component of sewer gas—can pose an explosion risk in enclosed spaces. If you smell sewer gas in your home, ventilate the area and call a professional to locate, assess, and fix the problem, as it will not go away on its own.