What is GPF?

GPF, or gallons per flush, is a characteristic that refers to the amount of water in the tank. This determines the strength of the flush, and it seems that the larger the tank, the more powerful the flush will be. However, if you need multiple flushes, the savings go down the drain.

1.28 GPF vs 1.6 GPF

The main options are 1.6 GPF and 1.28 GPF:

• 1.6 GPF is the classic variant. It uses more water.
• 1.28 GPF, labeled WaterSense toilet, uses less water, saves money and water. In some regions it's legally required to install toilets with 1.28 GPF or less.

TOTO UltraMax® II One-Piece Toilet, 1.28 GPF

How GPF affects flushing

It is logical to assume that since 1.28 GPF was designed for low-water usage, it should do its job at least as well as, if not better than, the standard 1.6 GPF counterparts. In reality, however, it turns out that it is not always the case. For example, if you have long pipes, a low-GPF toilet may not drain enough and contribute to material buildup.

Other reasons for poor drainage

If the 1.28 GPF toilet does not flush efficiently, it may require several flushes to clear the bowl completely. This can be due to a poorly designed trapway or low-quality materials, which are common in cheap toilets.

Toto Drake® Two-piece Toilet, Elongated, 1.6 GPF

In the end, there is no specific GPF that is best for a toilet, so you need to look at specific models, and evaluate their advantages.