I U A ?

[MiniMonty]

There was a ship.
It sank.
It sunk.

On the ship which sank / sunk some people remained on deck and they sang / sung.

On hearing the news of the disaster a lot of people turned to drink, they drank a lot and were drunk.

Does ANYONE have a rule (or even a habit) to deal with sink/sank/sunk etc

???

I think it's 'u' for passive tense i.e. the verb was done by someone else.

The ship sank - the ship does the sinking.
It was sunk by a reef - the reef does the sinking.

Some people sang. Songs were sung.
People drank. The beer was drunk.
Drunk in 'the people were drunk' is an adjective.