Often basement flooding is caused by two sewer systems
being interconnected. Some houses have downspouts, footing
drain, and/or the sump pump connected to the sanitary sewer
service. During a heavy rain, storm water enters the sanitary
sewers, causing backups into one house and overloading the
main lines, contributing to backups in other houses.
Sewer backups can also be caused by events not related to
storms or flooding. Individual service lines can be plugged by
grease, waste, tree roots, breaks in the pipe, or saturated
ground. Proper maintenance, like pouring tree root killer down
the toilet each year, can prevent most of these problems. The
sewer mains can also become plugged by the same causes as well
as vandalism or illegal placement of items in manholes. These
problems can be fixed by the owner or the City, depending on
where the stoppage occurs.
This guide focuses on protection measures that deal with
sanitary sewer backup that occurs when the sewer main is
overloaded and backs up through the sanitary service line into
There are four ways to stop sewer backup: floor drain plug,
floor drain standpipe, overhead sewer, and backup valve. Each
of these measures work for buildings with basements or
Floor Drain Plug
The simplest way to stop sewer backup is to plug the
opening where it first occurs. This is at the floor drain, the
sanitary sewer systemís lowest opening in the house.
Commercial plugs are available and can be placed in the floor
drain below the grate. Bolts on metal end pieces are tightened
causing a rubber gasket to expand and seal the plug in the
A plug stops water from flowing in either direction.
Therefore, if the laundry tub overflows or other spillage
occurs, it will stay in the basement unless the plug is
removed. Because of this, it may be best to leave the plug out
under normal circumstances and put it in place only during
The advantage of the plug is its low cost and ease of
installation. A standard floor drain plug can be purchased at
most hardware stores for $5-$10.
One variation is a plug with a float. It allows water to
drain out of the basement. When the sewer backs up, the float
rises and plugs the drain. A float plug permanently installed
will not interfere with the drainís normal operation.
A plug left in the flood drain may contribute to a wet
basement if spillage cannot drain out. Float plugs are known
to have been jammed open by a small amount of debris.
A floor drain does not stop backup from coming out of the
next lower opening, like a laundry tub or basement toilet.
Sealing the base of the toilet to the floor will protect you
until the water backs up higher than the top of the bowl.
A plug does not tell you if there is a problem in your
sewer line. If the plug is not tight enough, pressure can
eject it. In older houses, the sewer lines under the basement
floor may be clay tile. A buildup of pressure can break them.
In new houses, they are cast iron under the floor and less
likely to break.
A standpipe is an inexpensive alternative to a floor drain
plug. A "donut" with metal end pieces and a rubber
gasket in the middle is placed in the floor drain. A length of
pipe is placed in the "donut hole." The
"donut" can be purchased for about $10. A three-foot
length of pipe costs less than $5.
When the sewer backs up, the water stays in the pipe. Water
pressure can build up to blow a standpipe (if properly
installed) out of the floor drain. The system works unless the
backup is so deep that it goes over the top of the pipe.
One advantage of the standpipe over the floor drain plug is
that the overflow acts as a safety valve. Flooding in the
basement equalizes water pressure on the walls of the floor,
minimizing the chance of a cracked floor from broken pipes
A standpipe left in the floor drain may contribute to a wet
basement if spillage cannot drain out. A standpipe only
protects up to its height, normally three feet. Deeper
flooding will flow over the top. (A taller standpipe is not
recommended because it can result in too much water pressure
on your pipes).
An overhead sewer acts like a standpipe but without the
problems. A sump is installed under the basement floor to
intercept sewage flowing from the basement fixtures and the
basement floor drain. An ejector pump in the sump pushes
sewage up above the flood level. From there it can drain by
gravity into the sewer service line. Plumbing fixtures on the
first floor continue to drain by gravity to the service line.
It is unlikely that the sewers will back up above the
ground level. If water does go higher, a check valve in the
pipe from the ejector pump keeps it in the pipes. Backed up
sewage is enclosed in the sewer pipes so there is no worry
about overflowing laundry tubs or basement toilets.
The ejector pump requires maintenance and electricity to
work properly. The basement is disrupted during construction.
The contactor may have to run the overhead pipes through one
of more basement rooms, although often they can be
camouflaged. This work requires a licensed plumber and a
During a power outage, the ejector pump won't work. But
this only limits the use of the facilities in the basement
that need the pump. The upstairs plumbing still works and the
sewer is still prevented from backing up.
Although more dependable than a standpipe, an overhead
sewer is typically more expensive. A plumbing contractor must
reconstruct the pipes in the basement and install the ejector
pump. It typically costs $2,000-$5,000.
A backup valve stops the water in the sewer pipes. Older
versions of the approach were located in the basement and
relied on gravity to close the valve. If debris got caught in
the flapper, the valve did not close tight. Because of its
unreliability, valves were discouraged and even prohibited in
some communities. A newer "balanced valve" has
corrected these design shortcomings. A system of
counterweights keeps it open all the time so debris wonít
catch and clog it. When the sewer backs up, instead of relying
on gravity, floats force the valve closed. It is usually
installed in a manhole in the yard so there is less disruption
during construction and no concerns over breaking the pipes
under the basement floor.
As with overhead sewers, a valve is fully automatic. It can
even work when there is surface flooding. The owner can still
use the sanitary sewers during flooding as long as there is
power to run the ejector pump, which forces wastewater into
the sewer line when the valve is closed.
The ejector pump and valve require maintenance. This work
requires a licensed plumber and a building permit.
The cost of this type of backup valve is comparable to the
cost of an overhead sewer, in the $3,000 to $5,000 range.
This guide is designed to give the reader an overview of
things that can be done to protect a property from damage from
the type of surface water flooding and sewer backup that faces
many residents in the City of Wood River. The information
provided is based on careful research and input from
experienced professionals. The reader must assume
responsibility for adapting this information to fit his/her
conditions. This guide is not intended to replace the advice
and guidance of an experienced professional who is able to
examine the building and assess the needs of the particular
For more information, contact the Department of Public
Services at (618) 251-3122 or the Department of Building &
Zoning at (618) 251-3100.