First let me provide an explanation of how the system works. Fear not, we will keep the discussion to just "solids" and "liquids". Everything that goes down the drains in your house makes its way to the septic tank. This is a large, generally concrete tank. (Older ones might be steel). The waste enters the tank near the top of the tank. There are a pair of baffles in the tank to keep the solids in the tank, preventing them from flowing out of the tank with the liquids. Now, there are some solids that sink.. and some that float. Bacteria in the tank break down the solids as much as they can into a liquid form and this with the water entering the tank leaves the tank on the other side of the baffles. The liquid then flows to a leach field or a dry well where the liquid enters the soil and is absorbed by the ground.
As long as things are working properly, no solids make their way to the leach field and the soil absorbs all the liquid that winds up there.
Ok, the solids in the tank that the bacteria can't break down build up over time. If these are not removed by periodic pumping, the tank will eventually allow solids to get washed out to the leach field and begin clogging the soil there. When the soil gets clogged enough.. the system will no longer handle a flush. With that kind of failure the whole leach field will need to be replaced including, often, replacing the soil. (read: VERY expensive).
The main way to avoid septic system failure is periodic tank pumping. You HAVE to do this. Systems can appear to "work" for a long time without maintenance. You may hear about a system that "crashed." This means that the septic system appeared to be ok for a long time, but was actually getting in so much trouble that by the time a problem was noticed it was too late to do anything about it. The system crashed and was beyond repair. When a tank is not pumped often enough, there is less settling time for waste entering the tank. Small bits of floating solids are then carried out into the leach field and begin clogging the soil. This will shorten and eventually end its life.
Tank pumping frequency depends on:
Tank size or capacity
The volume of wastewater (number of occupants)
Amount of solids in wastewater (garbage disposals)
The Table below lists estimated pumping frequency according to septic tank capacity and household size.
Estimated septic tank pumping frequencies in years
(for year-round residences)
Tank Household size (number of people)
size 1 2 3 4 5 6 7 8 9 10
--------------------Years between pumping----------------------
* Below the minimum size allowed in many jurisdictions
Note: More frequent pumping is needed if you use a garbage disposal.
Septic tanks will not fail immediately if they are not pumped. However, an un-maintained septic tank is no longer protecting the soil absorption field from solids. Continued neglect may result in system failure and even replacement of the soil absorption field. In some cases, site limitations may make replacement of the absorption field impossible.
I didn't make a mistake by leaving out a discussion of additives for your septic system. They are a waste of money (literally pouring it down the drain) and often do more harm than good.
So what does it cost to have your tank pumped?? Well that will vary by your location, but you can figure on between $100 and $200 dollars. And THAT is not money down the drain!