This is the 11034th most frequent Turkish word.
doldurmuştu
"He/she/it had filled."
Here, 'doldurmuştu' is used to describe a past completed action in which someone had filled something completely.
Dolabı tamamen yiyeceklerle doldurmuştu.
They had completely filled the cupboard with food.
In this sentence, 'doldurmuştu' indicates that someone had filled a book with stories, again showing the past perfect tense.
Anı defterini kendi hikayeleriyle doldurmuştu.
They had filled the memory book with their own stories.
This usage of 'doldurmuştu' shows that the action of filling the bucket was completed before the subsequent action (watering).