The Drains in Your House and What Not to Put Down Them

Why this matters

Every drain in your house joins every other drain before the water leaves, so a habit at the kitchen sink can become a backup in the basement shower. Most drain calls a plumber answers are not broken pipes; they are something that went down a drain and stayed. Understanding the shape of the system tells you which clogs are a nuisance at one fixture and which are a main line problem that needs you to stop using water in the whole house right now.

If sewage is already coming up into a tub, shower or floor drain: stop running water anywhere in the house, including the washer, dishwasher and toilets, keep children and pets away, and see How to Handle a Sewer Backup in the First Hour. If the water is near outlets, cords or appliances, do not wade in; turn off power at the panel only from dry floor.

How the drains in your house fit together

  ROOF VENT (lets air in so drains flow and traps
  |          do not siphon dry)
  |
  +-- toilet (trap built in)       UPSTAIRS
  +-- tub -- trap
  +-- sink -- trap
  |
 MAIN STACK (vertical pipe)
  |
  +-- kitchen sink -- trap -- disposal   MAIN FLOOR
  +-- dishwasher (drains via sink)
  +-- washing machine -- standpipe -- trap
  |
 BUILDING DRAIN (under the floor or slab)
  +-- basement floor drain -- trap   LOWEST POINT
  |
 [CLEANOUT] capped opening for clearing the line
  |
 SEWER LATERAL (yard, under the ground)
  |
  +--> CITY SEWER MAIN    or    --> SEPTIC TANK

Three ideas in that picture explain most drain problems.

• Each fixture has a trap, a bend that holds a plug of water to keep sewer gas out of the room. A clog right at the trap affects that one fixture only. See Smells in the House and What Each One Might Mean for what happens when a trap dries out.
• Everything ends up in one pipe. The building drain and the sewer lateral carry the whole house. A clog there affects every fixture upstream of it.
• Water finds the lowest opening. When the main line is blocked, water from upstairs fixtures backs up and comes out at the lowest drain in the house first: usually the basement floor drain, a basement shower, or a first-floor tub on a slab home.

What not to put down them, and why each one causes trouble

How a little adds up. Say a household pours one cup of bacon grease a week down the kitchen sink. That is 52 cups a year, and at 16 cups to a gallon, a little over 3 gallons of fat in the line every year. It does not all stick, but the part that does stays, and it collects in the same cool, slow stretches of pipe each time. That is why a grease clog often appears years after the habit started. A jar or can for cooled grease, emptied into the trash, ends the problem.

How a garbage disposal actually works

A disposal has no blades. It has a spinning plate with two small swiveling lugs (impellers) that fling food against a stationary grinding ring around the edge, which shreds it into small particles. Water then has to carry those particles all the way down the line.

• Run cold water before, during, and for several seconds after grinding. Cold water keeps any fat solid enough to be chopped and carried rather than melted and spread.
• Feed it a little at a time, not a full sink of scraps at once.
• Keep fibrous scraps, grease, grounds and bones out of it (see the table above). It grinds them; the pipe still has to carry them.
• If it hums but does not turn, switch it off at the wall switch before doing anything. Many disposals have a reset button on the bottom and a hex socket in the center underneath for freeing a jam with the wrench that came with it; follow the owner's manual for your unit. Never put a hand into the disposal, even with it off; use tongs to remove an object.
• On a septic system, a disposal adds a lot of solids to the tank, which usually means pumping the tank more often. Ask your septic contractor before installing one.

The Saturday backup case, worked through

What happened. In a two-story house on city sewer, the kitchen sink has been draining slowly for a couple of weeks. On Saturday morning, the washing machine starts its drain cycle. A minute later, the downstairs toilet gurgles, and the basement floor drain bubbles and lets out a little gray water onto the floor.

Reading the signs in order.

1. One slow fixture for weeks, alone, is a local clog: in that fixture's trap or branch. A slow kitchen sink alone is very often grease.
2. A toilet gurgling when another fixture drains means air is being pushed through that toilet's trap, because water from the washer could not get past a blockage downstream and was pushing air ahead of it.
3. The lowest drain in the house letting water out is the clearest sign of all. Washer water could only reach the basement floor drain by going down the main stack, hitting a blockage, and backing up into the lowest opening.

Two other fixtures reacting to one drain event, on two different floors, points past the kitchen branch to the shared building drain or the sewer lateral.

What they did. They stopped the washer, asked everyone in the house not to flush, shower or run any water, kept the kids out of the basement, and called a plumber, telling them exactly what happened in the order it happened. They did not pour a chemical drain opener into the floor drain. On a main line clog it does not reach the blockage, it sits in the backed-up water, and it then splashes onto the plumber who opens the cleanout.

What was found. The plumber ran a drain cable through the cleanout and found the lateral blocked about 40 feet out with a mat of wipes held together by grease. The slow kitchen sink turned out to be its own grease buildup in the kitchen branch, from the same habit that put grease in the lateral; the wipes from the upstairs bathroom made the final plug. The plumber cleared both.

What would have changed the call. If only the kitchen sink were slow and nothing else reacted when the washer drained, it is a local clog, and a plunger (with the dishwasher drain hose clamped or the second sink basin covered) or a call at your convenience is reasonable. If the house is on a septic system, the same main line signs can also mean a full tank or a failing drain field, which is a septic contractor's call, not only a plumber's. If tree roots are common in your area, or the line is old clay or cast iron, the plumber may recommend a camera inspection to see whether the pipe itself is cracked or sagging (see Whose Pipe Is It? What the Utility Owns and What You Own for who pays for which section).

If your drains go to a septic tank

A septic tank is a buried tank where solids settle to the bottom, grease and light material float to the top, and the liquid in between flows out to a drain field, where the soil finishes treating it. Everything in the table above is worse for a septic system than for a city sewer, because whatever does not break down stays in your tank until it is pumped, and grease or fine solids that escape the tank can clog the drain field, which is the expensive part to replace.

• Spread out heavy water use. Five loads of laundry in one afternoon can push water through the tank faster than solids can settle. Spreading them over the week is easier on the system.
• Skip the additives. EPA guidance for homeowners says additives are generally not needed for a properly working system, and some can harm it.
• Know the pumping schedule. EPA suggests having a household system inspected by a professional at least every three years, with pumping typically every three to five years; the right interval for yours depends on tank size and household size, and your septic contractor will set it.
• Watch for the drain field signs: soggy or unusually green grass over the field, sewage odor in the yard, or every drain in the house slowing at once.

Your part, and where it ends

Your part: keep grease, wipes and the rest of the table out of the drains; run disposals with cold water; refill rarely used traps; know where the cleanout is (often a capped pipe near where the drain leaves the house, in the basement, crawlspace, or outside by the foundation); plunge a single slow fixture; and stop all water use when more than one fixture backs up at once.

The plumber's part: cabling or jetting a main line, opening a cleanout on a backed-up line (it can release sewage under pressure), camera inspections, repairing or replacing pipe, and septic problems with a septic contractor.

References

• See related: How to Handle a Sewer Backup in the First Hour
• See related: Smells in the House and What Each One Might Mean
• See related: Whose Pipe Is It? What the Utility Owns and What You Own
• See related: When to Stop and Call a Licensed Pro Around the House
• Your local sewer utility or septic program's guidance on what may go down drains in your area