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How Can I Tell if My Septic Tank is Full?

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Full septic system

Many septic system owners want to know when their tank is full so they know when to schedule a pumping. The problem is there are multiple definitions of a “full” septic tank, and only one way — opening the tank lids — to confirm it. Just because a septic system appears to be functioning properly, doesn’t mean it’s not full and in need of a pumping.

Defining a “full” septic tank

There are three ways your septic tank may be considered “full.”

Tank is filled to normal level

At this level, the tank’s outlet pipe allows liquids to flow in your septic system’s absorption area. The water level falls when the septic tank is pumped, but fills back to this normal level as the system is used.

Sludge has accumulated

As the tank reaches its normal fill level and the system continues being used, toilet paper and waste accumulate and get “trapped” in the tank (liquids continue flowing out of the outlet pipe to the absorption area).

Some of this paper and solid waste breaks down, but it cannot all magically disappear by itself — the septic tank must be routinely pumped and this sludge removed (most septic tanks should be pumped every 3-5 years).

Tank is “overfull”

A septic tank is considered “overfull” when the water level is at the very top of the tank. If the septic system’s absorption field stops accepting the water, it sits in the outflow pipe and backs up, overfilling the tank.

Preventing a full septic tank

No matter how long it’s been since you last pumped your septic tank, it’s “full” to a certain degree. But if it’s been 3-5 years since you last had it pumped, it’s probably time to do so.

Don’t wait until you have a problem to pump out your tank — by then, it’s usually too late to solve anything. Waiting too long between pumpings allows the sludge to continue accumulating, and can cause damage to your drainfield.

Schedule your septic tank pumping

Van Delden Wastewater Systems has been installing and maintaining septic systems in the Texas Hill Country since 1937. Give us a call at 830.249.4000 (Boerne) or 210.698.2000 (San Antonio) to schedule a septic pumping.


4 thoughts on “How Can I Tell if My Septic Tank is Full?

  1. I live with my grandpa. And only one bathroom has issues with the toilet flushing and sometimes the water draining out of the tub. Other bathroom toilet will flush only if you plunge. We tried flushing out pipes as best as we could. But nothing seems to work. Wondering what should we do???

    • Has anyone checked the septic tank? If there is backup in the tank (meaning the drain field is not accepting the amount of wastewater introduced into it), then you will still have a problem even if you clear the plumbing pipes. I would call a reputable septic pumping company, when they come out, ask them where the liquid level (not the sludge level) in the tank is upon arrival in relation to the outlet pipe. If the liquid level is above the outlet pipe, that is a strong indication that your drain field is failing. If the liquid level in the tank is not above the outlet pipe, then maybe you have a blockage between the house and the tank, or another issue going on before the wastewater even enters the tank. Good luck!

  2. We recently had a back-up of our septic. The tank had overfilled and was backing up into the pipes. We only moved in a year and a half ago and came from a town with sewers, so we were unprepared. Assuming that the previous owners hadn’t pumped recently, could it merely just be that it really needed to be pumped, or is the system really failing, as the guy who came indicated?

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