They generally dont expell fluids no. The need to conserve hydration in the body has meant that most terrestrial and arborial reptiles have biologically adapted the renal system for maximum performance.
Waste is basically filtered and solidified and water recycled.
They defecate this solid urinary waste, called urate' along with excrement, as a white chalky substance, which might be moist or dry depending on species, climate etc.
When a lizard is dehydrated (less water in the body) the urate becomes progressively yellow and then orange, since it becomes more concentrated.
As explained above, the condition of the lizards urate is a great indicator of its hydration status.