How Basement Floor Drains Work – Do You Need One?

As long as your basement floor drain is working as designed, you will hardly ever think about it. It will however trouble you if it is clogged or there is sewage backing up to your basement through it.

A basement floor drain is a drain on the lowest point of the basement designed to drain any water on the floor. This could be water from a leaking water heater, seepage after a heavy downpour or HVAC condensate.


If there is standing water in your basement, it is a sign that the basement floor drain is clogged. It could also be caused by a faulty sump pump if the basement floor drain is connected to the sump pit.

On the other hand, if you notice sewage backing up from your basement floor drain and pooling around it then the sewer line is clogged. In this case turn off water to your house and contact a professional plumber immediately.

If you experience water seepage in your basement after every downpour, you should consider installing a French drain around your house’s foundation. The French drain will channel the water away from the house keeping your foundation and basement dry.

Depending on where the basement floor drain is connected to, the water will go either into the sanitary sewer system or be channeled to the sump pit. In instances where the basement floor drain is lower than the sewer line, the water will go to a sewer pit with an ejector pump.

To prevent your basement floor drain from clogging, avoid dumping debris into it after sweeping the floor. Also make sure that the basement floor is always clean to prevent trash from being carried by water into it.

Do You Need a Floor Drain in the Basement?

So, is a basement floor drain that necessary? Is it something you can do without?

Yes! You need a floor drain in your basement. It removes water from the floor after a heavy downpour, condensation from the HVAC or leaking appliances like the water heater. This prevents damage to the house as well as growth of mold and mildew.

Unlike a toilet, tub or sink drain, which you will always need and use, basement floor drains are always out of sight and out of mind. This is why most people question their usefulness.

I can however guarantee you that the basement floor drain is like your health insurance. You hope to never use but should you need it your pocket will not be dented.

What do you think would happen if your water heater starts to leaks and you are away from home? Away from town even and you have no floor drain in your basement?

The Diagram

Image credit: Nations Home Inspection, Inc

From the surface, the only thing you can see is the cove grate. The drain connections are done underneath the floor of the basement.

The following are the components of a basement floor drain system:

1. Catch Bowl

A catch bowl is a basin underneath the cover grate which as its name implies catches debris preventing them from clogging drainpipes away from the floor drain opening. It is usually easy to remove the cover grate and clean the catch bowl from time to time.

Water and solids enter the catch bowl through the cover grate. The solids will then settle at the bottom while water will flow out via the drainpipe.

The drainpipe is installed at an angle to help the water flow out via gravity. This is unless the floor drain is under the sewer line where it would need to be pumped out.

It is important to regularly clean your catch bowl. If it is filled with debris, you drain will work as if one doesn’t exist and will therefore clog a lot.

2. Plumbing Trap


If your basement floor drain is connected to the sewer line, you will need to have a plumbing trap, also known as a P-trap or drain trap. If you want to know how a plumbing trap looks like, check underneath your kitchen or bathroom sink.

A plumbing trap is a curved section of the drainpipe which looks like a ‘U’ or inverted P. It is always (or should be) full of water.

That water acts as a barrier preventing sewer gases from coming up through the basement floor drain. Instead, the sewer gases are removed through the plumbing vent at the top of the house.

If the basement floor drain has not been used in a long time, the water in the plumbing vent will evaporate. Even if not all of it, enough to break the barrier.

When that happens, you will definitely have a sewage smell in your basement. What you should do in that case is to pour some water down the basement floor drain to replace that which evaporated.

3. Drainpipe

The drainpipe is responsible for carrying the water from the catch bowl to where you intend to drain it. While modern drainpipes are made from PVC, old drainpipes and catch bowls were made from cast iron or even clay tile.

When installing a basement floor drain, some people opt to include a cleanout. These cleanout works the same way as the sewer cleanout outside your house or elsewhere in the basement.

If you have such, you will see a large opening at the bottom after removing the cover grate. That is the drain hole.

You will also see another one on the side with a plug. That is the cleanout. The cleanout provides access to the drainpipe should you need to inspect or clean it after a clog.

As I had mentioned, the basement floor drain will be connected to one of the following 3 places:

Sewer Line

A sewer line is a large (usually 4-inch pipe) which runs from your house to the city sewer lines at the street. If you are on a septic system your sewer line will be connected to the septic tank.

Basement floor drains connected to a sewer line should definitely be connected to a plumbing trap. One thing to remember is that if the cleanout plug is missing sewer gases will still come out via the drain even if you have a trap. Replace the plug if it is missing.

When you have a basement floor drain connected to the sewer line, that is where sewage will start backing up from you have clogged sewer line. It is not pretty to have sewage pooling in your basement floor.

What you can do is to install a backflow valve. When sewage in the sewer line starts to flow back, a float connected to the valve will rise with it and seal the drain.

A backflow valve does not however fix a sewer line but it buys you time. Contact a professional plumber immediately and do not use any of your drains lest the sewage starts backing up from toilets, showers drains or sinks.

Sump Pit

A sump pit is basically a hole in the ground with a pump immersed inside of it. When water in the pit reaches a certain level, a float switch activates the pump which pumps the water out via a vertical pipe until the water level in the pit goes back to the required level.

Needless to say, backflow when your basement floor drain is connected to a sump pit is not problem for you. This is unless the sump pump malfunctions or in the event of heavy rains and the pump is overwhelmed or fails eventually.

It is important to remember that if your basement floor is connected to the sump pit you cannot drain waste which will negatively impact the environment. This is because sump pumps drain out into the environment without the water being treated first.

If you need to drain your washing machine wastewater (detergents present), water softener (salts present) or basement laundry sink you will need to connect the basement floor drain to the sewer line.

Sewer Pit

You connect your basement floor drain into a sewer pit when the sewer line is below the sewer line. In such a scenario the water cannot flow out via gravity.

A sewer pit is very different from a sump pit. A sewer pit comes with an ejector pump where the wastewater is pumped out into the sewer line.

Unlike a sump pit, you can drain wastewater from your washing machine, water softener and basement laundry sink into the sewer pit. This is because the wastewater will end up being pumped out and treated in a sewer treatment plant.

How to Unclog a Basement Floor Drain

Unclogging a basement floor drain is not as simple as unclogging a kitchen sink drain. You first need to understand how the drain works.

  • The first thing you will need to do is remove any pooling water. This is not a neat job but you should do it before it damages your house.
  • You will then remove the cover grate in order to access the drainpipe.
  • With the cover grate out, check if the catch bowl is full of debris. If it is scoop it out and trash it.
  • Introduce a drain snake into the drainpipe and crank the handle until you clear the clog.

In some cases you can clear a clogged basement drain using a plunger, baking soda and vinegar or even hot water but in most of the time only a drain snake will do it.

If it is the sewer line that is clogged and not the basement floor drainpipe then you will need to unclog it from the sewer cleanout. You can also call in a plumber if you do not feel too comfortable doing it.

And that is pretty much it in as far as basement floor drains are concerned. I hope this guide was helpful.

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