Run the test
Do this when the house is quiet and nothing else is using water.
- Start at the top.Run each sink for about thirty seconds, one at a time, starting with the fixture farthest from where the sewer leaves the house.
- Watch the low drains.While each fixture runs, have someone watch the lowest tub, shower and any floor drain for rising water.
- Flush each toilet once.Note whether it clears normally, and whether any tub or shower gurgles or rises.
- Record as you go.Mark each fixture on the table below as normal, slow, or causing a reaction elsewhere.
Worksheet
| Fixture | Drains normally? | Slow? | Water rises elsewhere? | Gurgling? |
|---|---|---|---|---|
| Kitchen sink | ||||
| Dishwasher | ||||
| Bathroom 1 sink | ||||
| Bathroom 1 tub or shower | ||||
| Bathroom 1 toilet | ||||
| Bathroom 2 sink | ||||
| Bathroom 2 tub or shower | ||||
| Bathroom 2 toilet | ||||
| Laundry standpipe or sink |
Reading your results
- IfOnly one fixture is slow and nothing reacts elsewhereThenFixture clog. See the kitchen or bathroom guide for safe first steps.
- IfEverything in one bathroom is slow but other rooms are fineThenBranch-line clog for that bathroom. A plumber can usually clear it from a cleanout or the tub overflow.
- IfRunning any fixture makes the lowest tub or shower riseThenMain-line clog. Stop using water and arrange for the main to be cleared.
- IfEverything drains but toilets gurgleThenPossible partial main-line restriction or a venting issue. Worth having checked before it worsens.
Why the lowest drain matters
Water follows gravity. In a single-story Fullerton slab home, the tub or shower nearest the point where the sewer exits is usually the lowest open drain, so that is where water from a blocked main shows up first. In a two-story house, a ground-floor bathroom plays the same role.
Knowing your lowest drain also tells you where to look during a backup, and which room to protect first with towels or by keeping the door closed.
Bring these answers to the plumber
- Which fixtures were slow, and which were normal?
- Did water rise anywhere else, and where?
- Is this the first time, or has it happened before?
- Where is the outdoor cleanout, if you have one?
Common questions
What if I only have one bathroom?
Watch the tub while you run the kitchen sink and the washer. If the tub reacts, the clog is past the point where those lines join, usually in the main.
Is gurgling always a clog?
Not always. It can also come from a blocked or missing vent. A plumber can tell the difference.
Can I run the dishwasher during the test?
Yes, but do it last and watch the kitchen sink and the low drains closely, since it pumps water quickly.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.