I’ve heard all kinds of advice about septic tank pumping and am more than flummoxed. Some of my neighbors have never done it, and others say it needs to be done frequently. When should you pump a septic tank and why? What happens if you forget or don’t do it when it needs to be done? The cost for septic tank pumping seems really high, and I’m wondering if it’s worth it.

Unfortunately, there is no definitive timetable for cleaning and pumping a septic tank. Many professionals who do this work will tell you it should be done every three years, but there are septic systems that probably should be pumped annually.

Let’s talk first about why septic systems need to be pumped. Wastewater from your home contains solids. Some of these solids break down and are devoured by bacteria in the tank. But think about it. When you wash dirty clothes, what happens to the small rock particles and dirt? They settle to the bottom of the tank.

Other solids that can’t be digested and broken down start to accumulate on the bottom of the tank, reducing the amount of water in the chambers of the tank. Furthermore, there’s a layer of scum where floating material like grease and lightweight solids start to accumulate. These also, over time, reduce the amount of water in the tank. You need water in the tank to fuel the breakdown of the solids.

If you don’t get sufficient breakdown of the solids in the tank, the small particles pass through the tank and are delivered to your leach field. The leach field is a critical part of the wastewater treatment system of a standard septic system. This field is comprised of perforated, interconnected pipes into which the effluent from the septic system flows. Usually the pipes are surrounded by sand or very loamy soil.

As the nearly clear effluent from the septic system passes through the sand and soil, the remaining pathogens are removed and safe water is the result. A septic system that is in good working order does not pollute the groundwater or the surrounding area.

But if solids are transported from the tank to the leach field because they are not broken down in the septic tank, over time the leach field will fail. If this happens, you will create a serious pollution hazard.

Regular pumping of a septic tank ensures you will not ruin your leach field. Replacing a leach field is an expensive proposition that costs thousands of dollars. The price to pump a septic tank is usually just several hundred dollars. It’s well worth the price.

The reason no one can give you a definitive schedule for pumping a septic tank is that it’s all a function of how large the tank is and how many people are discharging waste into the tank each day.

Most places that regulate septic system installation require you to get a professional septic design or plan produced before the system is installed. The designer takes into consideration the house’s size, or number of bedrooms, and total occupancy.

Using this data, the designer can size the actual tank. The trouble is, you may have purchased a home and have no idea whether the current tank is sized properly for the number of people living there. If this is the case, I urge you to hire a professional with years of experience with septic tanks. Frequently, a seasoned pro can tell the size of the tank after it’s pumped. Once he knows that, he can tell you how often it needs to be cleaned and pumped.

Tim Carter is a columnist for Tribune Media Services. He can be contacted at www.askthebuilder.com.