pinkeln
to pee
A colloquial expression for urinating or relieving oneself.
Der kleine Junge musste dringend pinkeln.
The little boy urgently had to pee.

to pee / to drizzle
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to pee
A colloquial expression for urinating or relieving oneself.
Der kleine Junge musste dringend pinkeln.
The little boy urgently had to pee.

'Pinkeln' (to pee) is a colloquial word. It is used in informal conversations with friends or family, but not in formal situations or in written language.
Kann ich kurz auf die Toilette? Ich muss mal pinkeln.
Can I quickly go to the bathroom? I need to pee.
Common and natural combinations are 'pinkeln gehen' (to go pee) or the phrase 'dringend pinkeln müssen' (to urgently need to pee) when you need a toilet quickly.
Die Kinder müssen vor der langen Autofahrt noch schnell pinkeln gehen.
The children need to quickly go pee before the long car ride.
When 'pinkeln' (to drizzle) describes the weather, the subject is always 'es' (it). It then means that it is only raining very lightly.
Ich glaube, wir brauchen keinen Schirm, es pinkelt nur ganz leicht.
I think we don't need an umbrella; it's only drizzling very lightly.
to make easier / relieve
'sich erleichtern' and 'pinkeln' can both mean that someone passes urine. The difference is mainly in tone. 'pinkeln' is colloquial and direct; you hear it in everyday life, especially in casual situations. 'sich erleichtern' sounds euphemistic and more indirect. It is used when you want to say it less directly. In normal conversations among friends, 'pinkeln' is more natural; in more careful wording, 'sich erleichtern' is more likely.

Das Kind muss dringend pinkeln, deshalb suchen wir eine Toilette.
The child urgently needs to pee, so we are looking for a toilet.
Vor der langen Busfahrt möchte sich die Gruppe noch kurz erleichtern.
Before the long bus ride, the group wants to relieve themselves quickly.