October 15, 1998
Septic Tanks Should Be
Cleaned Before Winter
By Tom Scherer,
Irrigation and Water Resources Specialist, Home Septic Systems
NDSU Extension
Service
Fall is a good time
to have your septic tank cleaned to make sure you don't have problems flushing
the toilet during the coming winter and early spring, according to a
"Periodic cleaning
of the septic tank is required maintenance for an individual home sewage
system," says Tom Scherer of the NDSU Extension Service. "Frozen and saturated
soil conditions slow the flow of effluent out of the tank, so getting the tank
into top condition before winter is a good idea."
The septic tank's
main purpose is to separate the solids from the liquids, allow bacteria to break
down the solids and store for removal the solids that don't break down. The
solids that stay in the tank, sludge, is mainly
composed of dirt (from washing clothes) and products of decomposition that are
heavier than water.
As sewage is broken
down in the septic tank, some solids settle to the bottom, and others float to
the top, Scherer explains. This separation produces three distinct layers within
the tank. The top layer is a scum composed of cooking fats and oils, soap
byproducts and products of decomposition which are lighter than water. Between
the sludge and the scum layer is the liquid layer. The liquid layer discharges
to the drainfield while the solids are retained in the
septic tank.
"When the sludge
that can't be broken down by bacterial action accumulates to a certain depth in
the tank, it must be removed," Scherer says. "Without removal, it will move with
the water to the drainfield. Those solids can plug the
field which will cause the effluent to back up into the house and/or rise to the
ground surface. Fixing either problem, especially in the winter, can be messy
and costly."
Most properly sized
septic tanks need cleaning about every three years. However, the actual time
will depend on the quantity of solids entering the tank. If you have a garbage
disposal in the kitchen sink, the tank should be cleaned every one or two years,
Scherer says.
If you are unsure
whether your septic tank needs to be cleaned, the sludge layer can be measured.
To measure the sludge layer in the bottom of the tank, secure 3 feet of white
terry cloth or toweling, rough side out, around a wooden or metal pole and push
to the bottom of the tank. Turn slowly two or three revolutions, let sit for a
minute then slowly withdraw. Sludge thickness can be measured where black
particles cling to the rough cloth. If the sludge is more than 12 inches thick,
have the tank cleaned.
Scherer discourages
the use of commercial products that claim to renew septic tanks through the use
of enzymes and special bacteria. Those components mainly affect the scum layer,
breaking it into smaller pieces which can get carried into the drainfield and contribute to plugging.
"Have your septic
tank pumped by a licensed contractor," Scherer says. "Cleaning a tank is more
than just pumping out the liquid. The scum and sludge layers must be broken up
by pumping and back-flushing the liquid into the tank several times. The mixed
contents can then be pumped from the septic tank and disposed of by an approved
method."
The only sure way to
effectively clean a septic tank is through the manhole, not through the
inspection ports (4- to 8-inch diameter pipes that come to the surface over the
inlet or outlet baffles). If the licensed contractor cleans the tank through the
inspection ports, he may break or dislodge the baffles, Scherer says. Breaking
the baffles can prevent free movement of effluent into and out of the septic
tank. When the septic tank manhole is open, have the contractor check the
condition, length, and submergence of the inlet and outlet baffles. If they are
corroded or broken, have the contractor replace them.
"For safety sake,
never allow anyone to go down into a septic tank unless a continuous fresh air
supply is pumped into the tank and a strong rope is tied around their chest,"
Scherer says. The person outside the tank must have enough strength to pull the
person out of the tank. Fatalities have occurred during septic tank maintenance
and repair because of the buildup of toxic gases.
Click
here for a pdf version of this graphic.
Click
here for a pdf version of this
graphic.