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Though the article addresses Lime Trees, the information will also apply to your Clementine Tree.

https://www.gardeningknowhow.com/edible/fruits/lime/is-lime-fruit-and-lime-blossoms-falling-off-tree-normal.htm
https://www.gardeningknowhow.com/edible/fruits/tangerine/mandarin-orange-tree-care.htm

Let them dry out, at least the top of the soil, before watering again. Make sure these receive full sun, and are fertilized every few months in container. You will also want to keep dolomitic lime, and iron sulfate around to prevent many problems that citrus face in container.

It is likely that you got a seed grown tree, instead of a graft. If this is the case, then you could expect another two or three years before it flowers. Just make sure to fertilize this at least once per year with a citrus fertilizer.

I would first suspect a water deficit. Water deeply and thoroughly.
But we would need more information on the growing conditions, soil and water management in order to offer better assessment and recommendatons.
Has the fruit always been dry, or is this a recent development?
If always, then it could be in the genetics of the plant and not much you can do about it. But if the fruit used to be moist and has developed the dryness in later years, then it must be related to watering and/or soil fertility.

My best guess here would be sodium toxicity. This is due to salty soil. This website will help you identify the problem further: http://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html

It would actually help to put down some potassium and phosphorus fertilizer, and some iron sulfate. This will help sweeten the fruit, as this can happen when the soil is lacking some trace minerals. Applying these will help the tree produce sweeter fruit, as it will replenish what is lacking in the soil.