Toilet tank parts (C) DanieL FriedmanSlow-Flushing Toilet FAQs
Questions & Answers Help Diagnose & Repair Poorly-FlushingToilets

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Slow flushing toilet diagnosis & repair FAQs:

These questions & answers about toilet flush problems help diagnose and repair toilets that flush too slowly or have a weak flush, or that are backing up.

The page top sketch identifies the key parts in the toilet flush tank or cistern. These parts control the flush water volume in both the toilet tank or cistern and in the toilet bowl. Other toilet flush problems besides inadequate flush water volume include blocked or partly blocked toilet drains or toilet drain line vents.

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Toilet Flush Problem Questions & Answers

Toilet tank fill line (C) Daniel Friedman

Question: dishwashing detergent & increasing the cistern water level helped clear up a slow flushing toilet

(Sept 11, 2014) Anonymous said:
My poorly flushing toilet problem was solved with the dishwashing detergent tip; then increasing the water level in the tank should help keep things moving along.
This is one of the best "how to" sites I have used. Thank you

[Click to enlarge any image] At left: the toilet flush tank or cistern usually contains a mark indicating the proper fill-line or water level in the flush cistern.


Thanks for the feedback Anon, it will assist other readers.

Question: bad smell out of drains when toilet is flushed

(Oct 15, 2014) Lisa said:
We just moved in the new built home and found out 3 toilets have same problems - weak flush and making a gurgling sound at the end. normally the problems will start from the a toilet in the powder room on the first floor then will affect the two toilets on the second floor at the next couple of days. The toilets are 1.6 Gal KOHLER. Any idea?

(Oct 16, 2014) lyndamae ooms said:
sometimes when i flush my toilet with the lid closed the toilet flushes and a little bit of toilet paper comes back up out of the hole looking a little chewed up. The toilet seems to be noisier when flushing. Irecently replaced the toilet flush valve with a new one but did not notice anything right away.

I am wondering why this is happening? we never had a problem before..

Also my house sunk about 1 and a half inches and it was raised again this summer... could something be broken inside all the plumbing inside the house or outside the house... the sewer pipe under the house going into the septic tank was severed from the house side.... and replaced with ABS sewer pipe to bring it up to code... it was about four inches from the house and four inches from the tank that was replaced. help i just don't know what to do.

(Jan 2, 2015) Anonymous said:
When the toilet is flushed, a really bad smell is coming out of every drain it seems. It is septic tank smell. I replaced the seal and it didn't help. The toilet does not flush completely and there is no smell when we use the sinks.


Anon noises or odors at nearby plumbing drains when a toilet is flushed often means that the plumbing vent system is blocked or incomplete.

Watch out: a sinking house would be expected to crack or break the drain piping as well as risking other even more dangerous conditions such as damaged gas piping or electrical wiring.

Question: toilet flushes better when pour a bucket of hot tap water into it

(Jan 3, 2015) Anonymous said:
What makes a toilet flush fine when pouring a bucket of hot tap water in it, but when flushed normally it drains slowly. Even when using a plunger it won't go down but when hot water is poured in it goes down fine ad no waste is left behind. I have used an auger and even did the enzyme treatment and no change.



Probably the volume of flush water and the speed of its delivery into the toilet bowl is what makes the difference. I've seen this problem in some older homes that used an under-sized drain line or in drains that were partly blocked by corrosion or deposits. Check that the plumbing vent system is functional while you're debugging this issue.

Question: toilet flushes then sewage returns back into the bowl

(Jan 5, 2015) Peter said:
my toilet when flushed seems to flush away waste then later it all comes back into the bowl?



How annoying.

You might see this if we have a pair of toilet troubles:

  1. The plumbing vent system blocked or incomplete
  2. The main drain is blocked downstream from the toilet

With this pair of problems a flush can send a bolus of water and waste down the drain, compressing air in the drain piping; but as the compressed air and sewage meet a blockage the air pressure sends the waste back to the toilet.

How quickly does the waste return. If it's almost immediately I suspect that there is a blockage close to the toilet. If it recurs later I suspect there is a blockage more distant down the sewer piping or in a private septic system - if your building is connected to one.

Is this problem unique to just one toilet in the building?
On what floor is the toilet?
How far below does the waste line exit the building: one floor, several floors, etc. ?
Are there gurgling or other noises when plumbing fixtures are drained?
Does the backup occur later as a result of other fixtures being run and drained?

Reader comment:

David said:

Don't forget to check other causes of a slow-flushing toilet, especially a clogged siphon jet (in the bottom, front of low flow toilets) or an obstruction in the vent pipe up on the roof. The four main causes of a slow flush are (Actually David listed five causes of slow toilet flush)

Not enough water in the toilet tank or cistern (not really - this doesn't cause a *slow* flush as much as an incomplete one - Ed)

Partly clogged drain (yes we discuss this above - ed)

Clogged rim holes around the toilet bowl (same effect as not enough water in the tank or cistern but you should indeed check for this - Ed.)

Clogged "siphon jet" (check in the toilet tank or cistern: if the small tube that sends water to the toilet bowl is not properly connected (sending water into the cistern or toilet tank instead) then the effect will show up as not enough water in the toilet bowl at the end of the tank or cistern fill cycle - Ed)

Clogged "air vent" (properly, this is a blocked, clogged, or missing plumbing vent, discussed in this article series - Ed.)

Question: My toilet drains slow when flushed.

(Feb 24, 2015) Exhausted Options said:
My toilet drains slow when flushed. I have snaked it, used enzyme treatments, cleaned the holes in the rim, adjusted the tank water level as high as possible. But I can pour a bucket of hot water into it and it goes right down....Any suggestions?



Often when I see the problem you describe, it's not the fact that the water is hot but that you're pouring a large dose of water right into the bowl that gives the toilet a better flush.

Start by pulling off the top of the toilet tank - don't drop and break it nor drop it on your toe.

Now after flushing the toilet, look closely at

1. The diverter tube during toilet tank/cistern re-fill after a flush. If the tube is not properly connected (it should be adding some water to the toilet bowl via the overflow tube as the toilet tank re-fills) then a result is too-low water level in the toilet bowl - this can give a poor flush even if the toilet tank or cistern was properly filled.

2. the water level at the complete end of the toilet cistern refill cycle: is the water level at the water line marked in the toilet cistern or tank? If it's below it that's a problem that can cause poor flushing.

3. When the toilet is flushed, check that the toilet flush valve flapper is not closing too early - which can happen if its pull / lift chain is too short and it's not opening fully when the toilet flush lever is pushed.

(Feb 24, 2015) Exhausted Options said:
- in regards to your reply;
#1 The divertor tube is putting water into the overflow tube and has the proper amount in the bowl ater the tank fills.
#2 I increase the water level in the cistern(tank) as high as possible with the adjustable fill assembly with the sliding stem float to the point that any higher and the fill valve will be hitting the tank lid.
#3 And as for the flapper closing too early I have even held the lever down through the whole flush sequence of filling of the bowl.

I have even did the liquid soap and also the CLR poured down the overflow tube--but not at the same time.

(Feb 24, 2015) (mod) said:

That sends us looking elsewhere.

Is this toilet the only slow one? Do others flush slowly ever? how about after several uses?

Do nearby drains gurgle when the toilet is flushed?

If so I suspect the venting system is blocked or defective.

I've disassembled toilets, messed with them, and finally pulled the whole toilet off of its mount to look for the causes of slow flush problems. We've pulled out underpants, cars, other toys that were blocking the toilet.

Feb 24, 2015) Exhausted Options said:
My house has 2 bathrooms that are back-to-back separated by a common wall. Both sinks, bathtubs, and toilet in the master bathroom are all fine or I would think the vent was clogged also. Plus I do not have any gurgling when flushing. Since I only have a 6" toilet snake my only option now is like you said and remove the toilet-- but if it's a blockage why would it drain down faster when pouring hot water (about 2 gallons) in from a bucket?


A longer drain power-snake cleanout is in order.

Question: toilet only flushes half of the water unless I hold the handle

(Mar 26, 2015) Anonymous said:
Just repaired inside of toilet. My problem is that the when I flush it only half of the water flushes. Meaning I have to hold the handle until flushes.

Reply: shorten the pull chain on the flapper valve


It sounds as if your flush valve is not properly adjusted - perhaps the pull chain is just a bit too long.


Apr 23, 2015) Anonymous said:
We don't flush the toilet when we use it for urinating but now it flushes poorly when we uses it for bowel movement. What is the cause of flushing poorly? It should work better when we seldom use the toilet paper. Please advise.


Check the water level in both the toilet bowl and tank; one of them is too low.

Question: How do I fix a slow flushing toilet that is not clogged

(Oct 4, 2015) Chris C. said:
How do I fix a slow flushing toilet that is not clogged on the main level while 2 toilets on the 2nd level flush normal?



The suggestions in TOILET FLUSHES POORLY apply to your case. Let us know if any of that is unclear or leaves you with questions.

Start by checking the volume of flush water in the toilet tank.

Question: Air bubbles in toilet bowl

(Oct 14, 2015) scott said:
Air bubbles in toilet bowl when flushed and doesn't fill fully. Need to hold down handle for 4-7 seconds.


Start by checking the volume of flush water in the toilet tank. Also check that the bowl fill tube that inserts more water into the toilet bowl as the tank fills is in fact connected to the toilet tank overflow tube - otherwise the toilet bowl won't re-fill to the proper level as the tank is filling.

Question: random bad toilet flushes

(Oct 21, 2015) Anonymous said:
randomly when flushing toilet, it will back up to rim. we have snaked it, nothing seems to resist the snake or comes up with snake. but will randomly flush good or back up to rim even with nothing put in toilet



When a toilet backs up to the rim sometimes but not always I'd look at what other water has just been sent down the same drain from the same toilet (subsequent flushes) or from other plumbing fixtures;

When there is a remote *partial* blockage downstream from the toilet and when no water has been run for a time, water has seeped past the blockage and the sewer line on the house side of the blockage is empty. Then the toilet flushes with no trouble. But when enough water has been run into the sewer line that it has backed up into the sewer piping on the house side of the blockage, then a toilet flush can back-up in the toilet, in nearby showers or tubs, or in other drains.

Question: harmful to flush dog doo down the toilet?

(Oct 29, 2015) Anonymous said:
Can putting dog poop down your toilet with a septic tank hurt it.



Question: toilet won't fill with much water

(Jan 18, 2016) Amy L. said:
We went away for 9 days while we were away there was a snow storm. When we returned. The toilet wouldn't fill with very much water. And wouldn't flush all the waist away. Often a backup would occur. All the other drains drain fine we even showered with no problem. So I feel it is an issue with the toilet. We poored water in the bowl but it just drains out. It seems it only holds about a couple of cups. Sometimes when we flush it an air bubble spits out of the drain. Help! I read everything on septic and toilets I tried everything that seemed connected.


Check for a clogged toilet fill valve. The tank needs to re-fill to the FILL LINE marked in the toilet tank.

Also check for cracks or leaks in the toilet bowl; usually these leak onto the floor but a crack might leak only into the building drain.

Question: toilet water level drops

(Mar 2, 2016) phil said:
after flushing the toilet and after filling back up to normal
then water level drops about 2 inches


If you mean water in the toilet bowl drops after filling then there is probably too much water being sent into the toilet bowl during tank-refill.

If you mean water in the flush tank drops, then there is probably a leak at the flush valve or at the tank mounting bolts.


(Mar 15, 2016)

Everlast said:
Nice blog. you clearly describe the guide to repair a toilet. We are a professional plumbing services firm to know more about us - Everlast Plumbing, Australia


Thanks Everlast Plumbing; while we do not allow posting of advertising links in comments, we welcome content suggestions, critique, corrections and at those occurrences we're happy to cite, credit, and give contact information for technical or professional contributors to the content of articles at; you can find our email at the page-bottom or page-top CONTACT link.

Question: toilet backs up after flush

2016/07/15 pinacoloda1 said:
My toilet bowl empties ok but then some of the contents come back up.,
Its not clogged,maintenance checked it. Always happens to me
not them,its very frustrating! So they're assuming everythings ok..


Sounds like a clogged drain that is causing backup when more water runs into the drain system; or if you're on a septic system the system may be blocked or failing.

There are several other reasons why a toilet fails to flush properly besides a clogged drain.



Toilet tank parts (C) DanieL Friedman

This sketch helps identify the toilet operating and repair parts we discuss in this article.

The Basics of How Toilets Work

While there have been improvements in toilet tank fill valves, flush valves, floats, and water savings, the design has remained about the same.

[Click to enlarge any image]

A flush lever moves an arm to lift a flapper valve or tank ball to permit water to rush into the toilet bowl below, washing away waste into the sewer pipe.

At the end of the flush cycle, a float arm, or a float moving on a vertical stalk (newer valves) drops to open a valve permitting the toilet tank to refill with water.

When the toilet tank water level reaches the proper level, the float closes the toilet tank fill valve.

Check for a Blocked Drain or Improper Venting

Low profile toilet (C) Daniel FriedmanIf the toilet always flushes, but it empties too slowly, or empties incompletely

This article series TOILET REPAIR GUIDE discusses the cause, diagnosis, and repair of toilet problems (water closet problems) such as a toilet that does not flush well, clogged toilets, slow-filling toilets, running toilets, loose wobbly toilets, and odors at leaky toilets.


Continue reading at TOILET FLUSHES POORLY or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see TOILET CLOGGED to diagnose and fix a blocked or clogged toilet


If the toilet is totally blocked and not flushing, see TOILET DRAIN CLOGGED

At PLUMBING DRAIN VENTS we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises.

More details about plumbing drain line venting can be found at PLUMBING VENT CODES & DEFINITIONS, also PLUMBING VENT DEFECTS & NOISES and at CLOGGED DRAIN DIAGNOSIS & REPAIR.

Also see WHAT CAN GO INTO TOILETS & DRAINS? both to avoid clogging drain lines and to avoid septic system damage if your building's wastewater is disposed-of on-site.

Or see these

Toilet Repair Articles

Suggested citation for this web page

TOILET SLOW FLUSH FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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