Why your low flow toilet may not flush properly

Answer:  If you've eliminated (pun intended) the possible causes of (1) maladjusted float and/or flapper, (2) partially blocked sewer line, and (3) abnormally low water pressure in your home (which may cause slow tank filling), the cause of your toilet misery may simply be poor engineering of the toilet itself.

In order to evaluate that possibility, check the size of the flapper, because this is key. Larger flappers such as the one on the left are good.  Smaller flappers like the one on the right are not so good.  I'll explain why in the sections below.  

Federal standards currently mandate that toilets use not more than 1.6 gallons per flush.

This is the stamp on the toilets that were builder-installed in our house, which was constructed in 2010.  The toilets themselves bore a September 2009 manufacturing date.  The problems with these things have persisted well beyond what EPA reports in terms of time frame.  EPA likes to claim that it was only the "first generation" low flow toilets back in the 1990's that caused problems.  We have evidence to the contrary.  

What seems to have happened is that, in order to meet federal regulations, some (but not all) manufacturers down-sized both the toilet tanks and the toilet bowls, but neglected to correspondingly up-size the throughput velocity of the flush mechanism.

This is most easily seen in the size of the flapper.  In the comparison photo above, I used an American quarter dollar to show two flappers to the same scale.  The water-stained flapper on the right is found within one of our builder-grade toilets that we just replaced this past weekend.  The shiny new flapper on the left is from that new replacement toilet.  You can immediately see that the replacement toilet has a much larger flapper.

A smaller flapper equals smaller water piping equals more sluggish flush speed, which may have been perfectly OK for as long as larger water volumes were still being used in older toilet models.  But when the water volumes were reduced, it became a recipe for toilet disaster.  A faster flush velocity is necessary to offset the reduced force brought by lower water volumes.  And a faster velocity is achieved by increasing the pipe diameter.

And unfortunately, there's only one workaround for a poorly-engineered toilet.

Rip it out and replace it.  What a waste (pun intended).  I will probably donate this via Craig's List or Clear Lake Freecycle, but given how poorly it functions, it'll likely end up in a landfill sooner than later.  All in the name of mandated water efficiency, probably thousands upon thousands of these things becoming solid waste of a non-biodegradable form, all across America.  

Our chosen replacement was the Toto Eco Drake.  My husband did the research on this product.  We had replaced the commode in our master bathroom with a Toto right after we moved in and were completely pleased with it, so we were sure that we wanted another of the same brand for our powder room.     

When I say "toilet disaster", I'm not really exaggerating.  We replaced our Master bath toilet immediately upon move-in because we realized that the toilets in this house simply did not function, and we had to have at least one of them that worked well.  It took a minimum of three flushes to clear the bowls of the builder-installed toilets, and often many more flushes than that.  One day, my husband became so infuriated with the performance that he used his iPhone to document flush by flush how long it took to achieve satisfactory completion of the task.  He did this because he figured that nobody would believe his description of just how badly the toilet worked, especially a toilet manufactured as recently as 2009, and so he needed proof.  He ended up with a sixteen-photo series, which in his state of high aggravation, he then forced me to view (the low point of my marriage, to be sure).  Sixteen flushes were required to get the job done - no kidding whatsoever.  I said to him, "I know you have an engineering interest in this predicament, but don't you dare post that mess on TexAgs!"
:-)

I suspect that there are at least 35 homes just in our section of the subdivision with the exact same brand of inefficient toilet installed.  Who knows how many homes nation-wide.  We feel your pain.  Take a deep breath (holding your nose if necessary) and get on with the business of toilet replacement.  You certainly won't regret it.

Our new Toto in its esteemed place.  We should have installed this four years ago when we replaced the one in our Master bath. Better late than never. Scratch another task off the 'to do' list.