Introduction

The bathroom sink is one of the most utilized fixtures in any home. Understanding how it is plumbed and how the various components work together is key to proper maintenance and being able to make repairs. In this comprehensive guide, we will take a detailed look at the anatomy of a bathroom sink plumbing system.

Anatomy of a Bathroom Sink Plumbing System

There are two main types of bathroom sinks – pedestal and vanity. While both utilize the same basic plumbing components, they are installed somewhat differently.

Pedestal Sink

A pedestal sink has the sink basin mounted on a pedestal above the floor. This allows for the trap and drain to be accessed underneath the sink for repairs and maintenance.

Sink Basin – Mounted to the wall and/or pedestal. Collects water used for washing hands, brushing teeth etc.
Faucet – Handles control hot and cold water flow into the basin. Faucet mounts to backsplash or countertop.
P-Trap – Shaped like the letter P, this curved section of drain pipe holds water to prevent sewer gases from entering through drain.
Drain Tailpiece – Short, vertical length of pipe that connects p-trap to sink drain.
Supply Lines – Flexible water lines connect faucet to hot and cold water supplies.
Shutoff Valves – Allow water supply to be shut off to replace faucet or supply lines.
Drain Pipe – Carries wastewater from p-trap down to main sewer/septic line.

Vanity Sink

A vanity sink is mounted into a countertop with the p-trap and drain accessed through a cabinet underneath.

Sink Basin – Mounted to countertop. Collects water used for washing hands, brushing teeth etc.
Faucet – Handles control hot and cold water flow into the basin. Faucet mounts through holes in countertop.
P-Trap – Shaped like the letter P, this curved section of drain pipe holds water to prevent sewer gases from entering through drain.
Drain Tailpiece – Short, vertical length of pipe that connects p-trap to sink drain.
Supply Lines – Flexible water lines connect faucet to hot and cold water supplies.
Shutoff Valves – Allow water supply to be shut off to replace faucet or supply lines. Often located inside cabinet.
Drain Pipe – Carries wastewater from p-trap down to main sewer/septic line. Accessed through cabinet.

Water Supply System

Getting pressurized hot and cold water to the sink faucet is an important part of proper operation. Supply pipes run inside the walls bringing water up from below or down from above.

Shutoff Valves

Having shutoff valves on the hot and cold water supply lines allows you to turn off water to the faucet to make repairs. These valves provide isolation to that fixture only.

Supply Lines

Flexible braided stainless steel supply lines are used to connect the shutoff valves to the faucet. This allows ease of installation and replacement if needed.

Faucet

The sink faucet controls the flow and mixing of hot and cold water into the sink basin. Single handle faucets use cartridges and discs while two handle faucets use rubber washers. Replacing these internal parts often fixes leaks.

Backflow Prevention

Codes require backflow preventers to be installed on supply lines. This prevents contaminated water from flowing backwards into the fresh water system. Common types are vacuum breakers and check valves.

Drain System

Proper draining of wastewater down the drain pipe is another key component. Correct installation and maintenance prevents leaks and clogged drains.

Sink Strainer

The sink strainer prevents large debris from entering the drain. It screws into the sink opening and uses a basket to catch particles, food etc. This basket should be periodically cleaned out.

Tailpiece

The tailpiece is a short, vertical section of pipe that connects to the threaded outlet of the sink strainer. It fits inside the curved p-trap underneath.

P-Trap

This curved section of drain pipe holds several inches of water in it at all times. This water prevents sewer gases from coming up through the drain. It gets its name from the p-shape.

Drain Pipes

Drain pipes carry wastewater and sewage from the p-trap down to the main home drainage line and out to the municipal sewer or septic system. ABS and PVC plastic are common.

Vent Pipes

Required vent pipes bring fresh air into the drain system to prevent vacuum lock and allow drains to flow freely. Often tie into the main stack vent line.

Cleanouts

Cleanouts provide access to the drain pipes for cleaning and maintenance. Caps thread out allowing snakes and augers to clear clogs. Should be located every 50 feet.

Common Problems and Repairs

While bathroom sink plumbing systems are relatively simple, issues can arise over time. Knowing the common problems and how to fix them saves time and money.

Clogged Drains

Slow draining or fully clogged drains are a common issue. Causes include accumulation of hair and debris in the p-trap or drain pipes. Using a zip-it tool or snaking the drain will generally get it flowing freely again.

Leaky Faucets

Faucet leaks typically come from worn washers or o-rings in the cartridge/valve body. These plastic or rubber pieces can harden or deform over time allowing water to leak when the faucet is off. Replacing cartridges/washers will stop the drip.

Leaky Pipes

Leaks in supply pipes, drains and trap assemblies often occur at threads and joints that loosen over time. Tightening fittings with pipe wrenches or applying new teflon tape or pipe joint compound solves many leaks.

Running Toilets

A constantly running toilet that won’t shut off can be due to problems with the float mechanism or flush valve seal. Adjusting the float arm assembly or replacing the rubber flush valve seal will stop the running water.

Low Water Pressure

Poor sink water flow can be caused by crimped supply lines, partially closed shutoff valves or heavy sediment buildup in faucet aerators. Inspecting lines and removing/cleaning aerators typically restores full pressure.

Drain Odors

Sewer gas smells coming from the drain indicate a dry trap from evaporation or a blocked vent pipe. Replacing water in trap or unclogging vent lines gets rid of the unpleasant odor.

Preparing for a Plumbing Project

Doing your own plumbing repairs or upgrades requires gathering supplies and safely shutting off water supplies. Planning ahead helps projects go smoothly.

Gather Supplies

Having the right tools and spare parts on hand will make your plumbing job easier. Stock up on common items like wrenches, plumbers putty, p-traps, couplings, primer & glue before starting.

Shut Off Water

The first step is to turn off the water supply lines using the angle stop valves under the sink or the main shutoff valve for the whole house. This prevents leaks while you work.

Protect Surroundings

Place towels around the sink and work area to absorb drips and leaks. Use drop cloths to cover floors and countertops. Remove items from under the sink so they don’t get damaged.

Take Pictures

Before disassembling the existing plumbing, take photos of the setup. This provides a useful reference when it’s time to put components back together.

Following these steps allows you to dive into a plumbing repair or replacement project with confidence!

Typical Maintenance

To keep your bathroom sink plumbing operating properly for years to come, perform these simple maintenance tasks periodically.

Remove sink strainer and clean out debris that has accumulated in basket. Rinse out any hair or gunk.
Check sink overflow opening for any debris or buildup blocking it. Use a small brush to clean opening.
Remove faucet aerator and soak in vinegar to dissolve hard water deposits and sediment. Rinse clean.
Inspect supply lines and angle stops for any drips or corrosion. Tighten fittings or replace if deteriorated.
Fill trap with water if any sewer gas odors are noticed to re-prime the p-trap seal.
Test sink drainage by pouring a few cups of water rapidly down the drain. If any gurgling occurs, plunging is needed.
Occasionally disassemble and clean the p-trap and drain tailpiece to remove sludge and buildup.

Common Problems and FAQs

Here are answers to some frequently asked questions about bathroom sink plumbing systems.

What causes my bathroom sink to drain slowly?

Slow draining usually occurs from a accumulation of hair, soap scum and debris in trap and tailpiece. Removing and cleaning the pieces restores normal flow. A clogged vent pipe can also cause slow drainage.

Why does my pedestal sink rock back and forth?

If a pedestal sink is not tightly bolted to the wall, it can rock and become loose over time. Tightening the wall mounting bolts and washers stabilizes the sink again. Shims can level if needed.

What do I do if my bathroom sink faucet leaks?

For a leaky two handle faucet, replacing the rubber valve seats and springs should stop the drip. On single handle models, replace cartridge or worn disks/o-rings. Fully shutting off hot & cold angle stops verifies the leak is in faucet.

Why does my drain keep smelling like sewer gas?

Sewer gas odors come from a dry p-trap. As water evaporates over time, it needs refilled. A blocked vent pipe can also cause air to bubble up through drain. Pour water in trap and snake vent to resolve.

How do I unclog my bathroom sink drain?

Start by disassembling and cleaning the p-trap and tailpiece. Use a zip-it plastic tool to pull hair from trap. For deeper clogs, use a drain snake or auger inserted in cleanout plug further down the pipe.

Can I install a bathroom sink and faucet myself?

With some plumbing experience, you can absolutely DIY a bathroom sink install. The key is proper preparation – turning off water supplies, assembling tools, disconnecting existing sink. Patience and following best practices keep the project manageable.

Conclusion

Understanding how your bathroom sink plumbing system functions is an important part of keeping it operating properly over time. Knowing the anatomy of the fixtures, supply lines, drains and venting allows you to tackle repairs yourself and perform routine maintenance. If persistent issues arise, don’t hesitate to call in a professional plumber to get things flowing freely again. With the helpful information in this guide, you can keep your bathroom sink area working properly for years of regular use.

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Understanding the Plumbing of the Bathroom Sink

Introduction

Anatomy of a Bathroom Sink Plumbing System

Pedestal Sink

Vanity Sink

Water Supply System

Shutoff Valves

Supply Lines

Faucet

Backflow Prevention

Drain System

Sink Strainer

Tailpiece

P-Trap

Drain Pipes

Vent Pipes

Cleanouts

Common Problems and Repairs

Clogged Drains

Leaky Faucets

Leaky Pipes

Running Toilets

Low Water Pressure

Drain Odors

Preparing for a Plumbing Project

Gather Supplies

Shut Off Water

Protect Surroundings

Take Pictures

Typical Maintenance

Common Problems and FAQs

What causes my bathroom sink to drain slowly?

Why does my pedestal sink rock back and forth?

What do I do if my bathroom sink faucet leaks?

Why does my drain keep smelling like sewer gas?

How do I unclog my bathroom sink drain?

Can I install a bathroom sink and faucet myself?

Conclusion

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