How often should you pump a septic tank?

Short answer

Pump the septic tank every 3 to 5 years. A large household, a garbage disposal feeding the tank, or a small tank for the size of the house shortens that to every 1 to 2 years. Pumping is a truck with a hose that empties the tank of sludge and scum, and it's strictly a professional job. It takes 60 to 90 minutes and costs $300 to $600.

Why it matters

The tank's job is to hold back solids so only water reaches the drain field. Solids settle to the bottom as sludge and build up slowly, and nothing removes them except the pump truck. As the sludge rises, the clear water zone in the middle shrinks, until solids start washing out of the outlet with the water on every flush.

Solids in the drain field are the one failure a septic system can't recover from. They clog the soil, the water backs up, and the field has to be dug up and replaced. The tank itself is a fraction of that cost, and pumping it on time is a fraction of that again. Pumping too late also lets scum and sludge reach the outlet baffle, which can break it, and leaves the tank's walls exposed to gases that corrode concrete. Regular pumping keeps the whole system in the cheap part of its life.

When to do it more often

A large household: more people means more solids, so the tank fills faster.
A garbage disposal: food waste adds a lot of solids to a tank that was sized for sewage alone, and some sources say it can double the pumping frequency.
A small tank for the house: an older tank, or one that was undersized when a bedroom was added, holds less and fills sooner.

In any of those cases, every 1 to 2 years. The inspector's sludge measurement is what settles it, since the right interval is whatever keeps the sludge from reaching the outlet.

What you need

Nothing. The pumping company brings the truck, the hoses and the tools. Knowing where the tank lids are, and having them uncovered, saves the crew time and you money, since some charge extra to find and dig out a lid.

Steps at a glance

Locate the tank's lids, and dig them out if they're buried, before the truck arrives.
The crew opens the lids and lowers the hose into the tank.
They pump out the liquid, the scum and the sludge, breaking up the sludge with the hose as they go.
They look at the empty tank for cracks, check the baffles, and rinse and replace the effluent filter if there is one.
They close the lids and note the date and the tank's condition for your records.
Leave the tank to refill on its own, which happens through normal use over a few days.

You're done when the tank is empty, the lids are back on, and you have a receipt with the date for your records.

Signs it's overdue

Sludge filling more than a third of the tank at the last inspection.
Slow drains through the house, or gurgling in the pipes.
A sewage smell outside near the tank, or inside from the drains.
Pooling water or a soggy patch over the tank or the drain field.

DIY or pro

This is a pro-only job. Nobody owns a vacuum truck, and the waste has to go to a treatment plant, which the pumping company handles under the proper permits. The one thing you can do that matters is keep records: the date of each pumping and the sludge depth the crew measured. The gap between pumpings, and whether the tank was full or only half full each time, tells you whether your interval is right.

Expect to pay $300 to $600. The price rises with the size of the tank, the distance the truck has to park from it, and whether the crew has to dig to find the lids. Installing risers that bring the lids to the surface is a one-time cost that makes every future pumping cheaper and faster.

Safety

Chemicals: a septic tank gives off hydrogen sulfide and methane, and the air just inside an open lid can knock a person down. Don't lean over an open tank, don't go into one, and keep children and pets well back while the lids are off. Leave the open tank to the crew.

FAQ

How do I know when my septic tank needs pumping?

The sludge measurement at inspection is the sure way. Between inspections, slow drains, gurgling, a sewage smell or a wet patch over the tank all mean it's time.

Can you wait too long to pump a septic tank?

Yes. Once solids reach the drain field, the field clogs and has to be replaced. That costs far more than every pumping the tank will ever need.

Do septic tank additives mean I can pump less often?

No. The bacteria the tank needs are already in the waste. Additives don't remove sludge, and some break up the scum so it reaches the drain field sooner.

How long does pumping a septic tank take?

Plan on 60 to 90 minutes once the truck is there, longer if the lids have to be dug out.