What is the ruling on the undesirability of turning off all the lights in the house when sitting, sleeping, or leaving it, and the undesirability of pouring hot water in the toilet except after saying "Bismillah" (in the name of Allah)? And is there any basis for this in religion to avoid evil spirits (shayatin)?

Turning off lights when sleeping is recommended in Islamic law. There is no harm in saying "Bismillah" (in the name of Allah) when pouring hot water, but it is better not to pour it in a place where one expects living beings to be present. Protection from devils is achieved by maintaining congregational prayers and consistently reciting the morning and evening remembrances (adhkar), as well as the adhkar for entering and exiting.