Jadnashua
Retired Defense Industry Engineer xxx
All modern toilets (with few exceptions) only drain part of the tank when you flush. If you insist on using more, you hold the handle down to drain the whole tank. This normally doesn't do anything more than waste water. You can call it dual flush, and some do, but draining the tank sort of violates the principle of low-flow, water saver. With any modern toilet, you fully depress the handle and immediately let go, and if it passed certification and you haven't modified anything, it uses the stated amount of water.
A true dual-flush toilet with decent specs will have either a shallower or narrower water spot than one that isn't. This is so that when you use the small flush, it can still evacuate the entire bowl - you don't want to just dilute what may be left, you want it gone. This is why retrofitting an old toilet with a dual-flush valve doesn't really work well - the bowl has more water in it, and the smaller amount allowed to get through on a flush isn't enough to fully empty the bowl, but it will dilute it considerably. Because a shallower water spot means a large deposit may not be covered, it can be smellier until it is flushed away. A deeper water spot can cover it, but then there's more opportunity to get skid marks along the way to it that may not wash off as well during the flush with the lower volume. There are tradeoffs you have to accept with a dual-flush toilet generally not needed with a good single flush one. Generally, the bowl will not stay as clean, depending on the consistency of your deposit and aim. On a Toto, SanaGlos helps, since it is quite smooth, stuff doesn't stick as much, and washes off easier. But, there is only so much a limited amount of water can do; unlike the old gully washers of old that might have used 5-8 gallons...
A true dual-flush toilet with decent specs will have either a shallower or narrower water spot than one that isn't. This is so that when you use the small flush, it can still evacuate the entire bowl - you don't want to just dilute what may be left, you want it gone. This is why retrofitting an old toilet with a dual-flush valve doesn't really work well - the bowl has more water in it, and the smaller amount allowed to get through on a flush isn't enough to fully empty the bowl, but it will dilute it considerably. Because a shallower water spot means a large deposit may not be covered, it can be smellier until it is flushed away. A deeper water spot can cover it, but then there's more opportunity to get skid marks along the way to it that may not wash off as well during the flush with the lower volume. There are tradeoffs you have to accept with a dual-flush toilet generally not needed with a good single flush one. Generally, the bowl will not stay as clean, depending on the consistency of your deposit and aim. On a Toto, SanaGlos helps, since it is quite smooth, stuff doesn't stick as much, and washes off easier. But, there is only so much a limited amount of water can do; unlike the old gully washers of old that might have used 5-8 gallons...