Bathroom Sink Drain Assembly and the P-Trap

Simple But Effective

Bathroom sink drains appear to be quite simple but believe it or not there is centuries of trial and error behind the design. Long before the p-trap, the problem that early drain manufactures faced was keeping sewer odors at bay.

Plumbers never found it difficult to drain water from your bath sink, mainly because any sloping downward drain worked fine just fine. The problem that the p-trap solved was keeping the smells of the sewer out of the house and from crawling back up your pipes.

As it were, the same pipes that carried the waste water to the sewer systems down below similarly carried the pungent and possibly dangerous sewer gas back up into your home. Fortunately for us, the p-trap effectively solved the odour and volatile gas problem.

Modern sink drain design has evolved with plumbing technology thereby making the installation of a new sink drain assembly relatively easy enough to be installed in an afternoon.

For centuries early plumbers tried to solve the drain problem, but it wasn’t until the 1800’s when the s-trap was invented that the drain problem was almost solved.

Keeping Sewer Gasses Out of Your Home

How the s-trap works is that when the low bend in the s-trap pipe is filled with water, it effectively acts as a plug in the drain pipes, thwarting the volatile sewer gases from seeping back up the sink drains and into the bathroom.

Now, this solution worked in theory, but unfortunately the rushing water going down the sink drain would create a vacuum sucking the remaining water down the bathroom drain with it, thereby effectively breaking the water seal in the drain pipes.

One solution to keep the sink drain sealed was that each time you used your sink, to re-establish the seal you had to remember to keep a jar of water handy to pour a little bit down the drain to fill the trap, and if by chance you forgot, you would be hastily reminded if you forgot by the rancid scent.

Finally, around 1874, a smart plumber figured out that all you had to do was to equalize the air pressure in the drain system to keep the water seal. The early plumber discovered that by adding another piped called a vent that ran upward to the roof, this created a kind of pressure relief system so that sewer gases wouldn’t stink up the house.

Putting it all Together

As plumbing technology got more sophisticated, afterward a more effective version of the vented s-trap called the p-trap was manufactured which ran down from under the sink, formed a “u” shape and then attached to the main drain pipe on an upward sloping horizontal to effectively keep water in the “u” shaped sealed. This new drain pipe design was respectfully christened the p-trap because it looked like a “p” lying on its side.

There were many other slight variations to the p-trap drain design but needless to say, the p-trap effectively solved the problem of bad odors coming back up your sink drain to pollute your bathroom.

Connecting your bathroom sink’s drain pipe assembly to your home’s drain plumbing system is a pretty straightforward process and can be completed as a do-it-yourself project in a matter of hours.

The good part about connecting your drain pipe is that no matter what type of sink you purchase, vessel or below the counter, the drain and water-supply connections are pretty much going to be installed the same way on all sink products.

Gather all the drain pipe assembly parts. First, you must tighten a female adapter (this is best initially done by hand tightening) onto the drain stub-out on your bathroom wall. Next guide slip nuts onto the pipe drain arm and the sink bottom’s tailpiece.

Now comes the p-trap. Connect a p-trap in place and also tighten the slip nuts by hand. Continuing on, when you connect your flexible water-supply lines onto your faucet’s tailpieces, make sure you track them to the shut-off valves.

Now that everything is in place, tighten the coupling nuts with an adjustable wrench using light but firm pressure. Once everything is secure, you can remove the faucet aerator and turn on your water supply.

As a final step, inspect the shutoff valves and pipe joints to make sure they are not leaking. Finally, turn on your faucets and inspect everything for potential leaks in the bathroom drain assembly. Replace the aerator, and you’re ready to use your bathroom sink.