I’ve heard some people say septic tanks need to be pumped only every 10 or 12 years. What do you think of that idea? Our septic code says every three years.

I have heard the same thing and I have some comments. I also sought the feedback of my friends in the septic service industry here in Minnesota.

I visited one of the Pumper online discussion forums (www.pumper.com). Posted comments said some designers and installers were proposing a 10- to 12-year cleaning frequency. I agree there may be conditions where a septic tank does not need to be cleaned for 10 years. But there also are conditions where a septic tank should be cleaned even more often than every three years.

Every septic tank is different. Solids build up at different rates. Kitchen sink wastes differ from home to home. Garbage disposers are not recommended for use with a septic system because they discharge raw materials. And they are prohibited by many state and local codes. But garbage disposers are sold to anyone, and a homeowner with a little plumbing savvy can easily install one without knowing they are detrimental to the septic system.

WHO LIVES HERE?

The number of people in a home will affect the solids accumulation. Most onsite systems are designed for homes with three or four bedrooms. A four-bedroom home might have two occupants or eight occupants. So the amount and nature of the sewage will differ a great deal from home to home.

Two people who are at work all day may occupy a home. There are not many sewage solids deposited in their septic tank during the week. A three- or four-bedroom house may be occupied only during the summer months by a retired couple. They spend their winter months in a warmer place. No sewage is deposited to the septic tank during that time. Their home likely has a large-volume septic tank or tanks. In my opinion, there is no way they will build up enough solids to require septic tank pumping every three years. Perhaps 10 or 12 years would be adequate here.

There are other complicating factors in sludge buildup. People from other countries living in the U.S have different standards. Sometimes more people occupy a house than the septic system was designed to handle. Food preparation, dish and clothes washing and toilet use will rapidly build up the sludge in such tanks. It is likely such a septic tank should be cleaned more often than every three years.

Septic tanks located in the warmer parts of the country will have a higher tank temperature. Higher tank temperature results in more active bacterial breakdown of the sewage solids. This will decrease the rate of sludge buildup.

WHAT ABOUT BIGGER TANKS?

Pumpers in my area note that people who are on chemotherapy will cause the septic tank bacteria to be less active. They also mention that an acne medication is harmful to bacteria in the tank. And anti-bacterial laundry soaps slow down bacterial action.

In Minnesota, the trend has been to require larger septic tank volumes. For three- or four-bedroom homes, one nearby county requires two 1,000-gallon septic tanks connected in series. Another county requires a 1,500-gallon compartmented tank. Tanks in series and compartmented tanks are more effective than a single tank in treating sewage. There is also more volume available for sludge storage.

In my opinion, such large volume tanks in series and compartmented septic tanks should not need to be cleaned as often as the 1,000-gallon tanks required by previous codes.

The amount of solids in a septic tank should determine if the tank needs pumping. The amount of sludge and scum in the septic tank should be measured near the outlet pipe.

A standard used for many years says the sludge layer should be no closer than 12 inches beneath the tank outlet baffle. The scum layer must be no closer than three inches to the bottom of the outlet baffle. Whoever measures the scum and sludge must have an accurate device.

One of our nearby counties allows sludge and scum accumulation to be measured by the homeowner. This may be a valid procedure if the homeowner is properly informed on the standards. The homeowner should be made aware that solids washing into the drainfield will shorten the life of the soil absorption field.

A water meter can also be used to evaluate septic tank usage. The volume of waste flowing to the septic tank can be measured in gallons. This would be an index of the amount of use and may be helpful in determining solids buildup. However, the nature of the sewage wastes will vary from house to house.

Outlet filters on the discharge line of the septic tank will prevent excess solids from flowing to the drainfield.­ One of the onsite contractors I know installs both a water meter and a septic tank outlet filter for every system.

BETTER SAFE THAN SORRY

Obviously there is no general rule on how often a septic tank should be pumped and cleaned. The “error of safety” would be to pump tanks more often than they need to be pumped.

The soil absorption system is the expensive part of an onsite system. The purpose of the septic tank is to send clean effluent to the soil absorption system. To pump and clean the septic tank more often than necessary may be an extra expense, but it protects the soil absorption system.

If the septic tank is pumped less often than it should be, the soil absorption system may have an early failure, resulting in a costly replacement for the homeowner. Perhaps it is better to be safe than sorry and pump the tank a little more often than it really needs.