Keep your drains flowing free – Part 1

April 2nd, 2014

Keep Your Drains Flowing Free

By Jerry Alonzy

Part 1 – Understanding how your drains work

We talk a lot about water quality and its relationship to health, but the fact is that only half of plumbing is water coming in. The other half is water going out, via your home’s drain or waste water system.


Image via Delta Faucet Company

Plumbing drains seem simple and I guess they are to those of us who have had their benefits for our entire lives. But your home’s drain pipes are not randomly placed… they follow design principles that have been in place for hundreds of years, ever since the recognition that gravity controls the movement of water!

A waste water drain system (regardless of the material it’s made from) must incorporate certain characteristics to function safely and effectively:

1) All drain pipes must slope downwards over their entire length. The slope must be steep enough so that waste-filled water will flow in the desired direction at adequate speed to allow all waste material to exit into the sewer or septic system.

If even a small section of drain pipe is level or, worse, sloped upwards, it will both slow the emptying of the pipe and become a “trap” where waste will tend to accumulate, leading to a blockage over time.

Some old homes that have experienced severe settlement develop drain problems due to loss of slope. Typically, modern plumbing standards allow for a bit of settlement without any deleterious effect on efficient draining, but if your home has persistent blockages putting a level on the pipes to verify the slope might not be a bad idea!

The required minimum pipe slope is not haphazard.  It is determined via plumbing standards or codes that are recognized nationwide, though some local areas have stiffer requirements based on local experience. Needless to say, the closer a drain is to vertical, the better!

2) Drain pipes must follow the rule of progressive sizing. Simply put, if there is a change in the size of the pipe, it must always go from smaller to larger. This is important because it guarantees that any solid or semisolid object moving through the pipe will not become stuck in the next section of pipe, at an elbow or at a pipe joint/connection.

  1. There is always a restriction of some kind at the beginning of the drain. This is to prevent certain type of objects (and occasionally small animals) from entering the drain system. Restrictions in kitchen drains are different from bathroom drains, which are different from showers or toilets. A combination of efficiency (speed at which the water can drain past the restriction) and typical usage (what types of items might go down the drain) determine the design of the restriction.
Image via Delta Faucet Company

Image via Delta Faucet Company

For example, kitchen drains are restricted by the slots in the metal “basket” to prevent tableware or rings from getting into the drain, while small food items can get past. If there is a garbage disposal, the design of the disposal is such that only very fine particulates can get by the grinding mechanism.

Since bathroom sinks also function as vessels to hold water, they incorporate a movable stopper system (called a pop-up) which acts as a restriction and also allows the sink to fill and drain easily. Though the pop-up can be discarded and a rubber plug used instead, the risk of dropping something down the drain (such as a ring or a toothbrush) is significant and, unfortunately, the repair can be daunting since the drain trap under the sink may have to be disassembled!

Toilets, on the other hand, are the least restrictive plumbing drain appliance. While a sink drain is 1 1/4 to 1 1/2″ in diameter, a toilet drain is 3 – 4″. In order for a toilet to function properly, especially low flow toilets, the water must exit the toilet with power and at good speed. Thus the need for a large water pipe!

-Toilet Pipes Map Image-

Image via Kohler Company

Image via Kohler Company

Though not obvious if you look into the toilet bowl, toilets do have a restriction built-in. If you look at a side-view of a toilet, you’ll see the serpentine path the waste takes as it flows from the bowl to the waste pipe. This is by design to catch any very large items, which will be hopefully spit back into the bowl. Certain items such as wooden matches and cotton swabs and larger, solid paper items can cause a clog within the toilet itself. In fact, most problems with toilet blockages are within the toilet itself and not in the drain pipes. For more on this and other common drain problems, stay tuned for Part 2 of this article!

Stay tuned for Part 2 – Solving Common Drain Problems


Author information:
Jerry Alonzy, a.k.a the Natural Handyman, has been an active handyman for over 30 years with experience in most areas of home repair and renovation. As a do-it-yourself author and web developer since 1995, he has been featured in USA Today, the Today Show and on radio shows, magazines, newspapers and websites, including his own at

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