Answer:
The right way to rewrite the sentence is the following one:
After I had spent all day cleaning the apartment, it was as sterile as an operating room.
Explanation:
We want to convey the idea of two things that happened at different times of a day, which means there was a chronological order in which those events took place. Therefore, we want to use two verb tenses:
Past Perfect Tense: for the event that happened first.
Simple Past Tense: for the event that happened some time after the first one.
Check it out:
Past Perfect (1st event) Simple Past (2nd Event)
↑ ↑
After I had spent all day cleaning the apartment, it was as sterile as an operating room.
