The Warmhearted Weasley Family

Once they had decided to use Grimmauld Place as their base, the first thing to do was naturally to clean it thoroughly, inside and out;

Pests like Doxies and Bandimangs existed in the Magical World, and to Wizards, they were much like cockroaches, termites, fleas, and mold in the Muggle World.

Grimmauld Place had been abandoned for more than ten years. Even with household magic and a House-elf, cleaning it properly would not be easy.

When Fred and George left, they said they still had a "secret weapon" that could make the cleaning twice as effective with half the effort;

According to Vizet and Luna's reasonable guess, this so-called "secret weapon" was probably Molly Weasley, Fred and George's mother.

Neville was still the first to arrive. As soon as Vizet and Luna entered Grimmauld Place, they saw Neville wiping breadcrumbs from the corner of his mouth before waving at them.

Before long, Hanna also arrived, carrying a large bag filled with magical cleaning agents, which were said to have come from Old Tom;

According to Old Tom, these magical cleaning agents worked extremely well. Supposedly, even grime that had built up for fifty years could be cleaned away.

Neville looked at the magical cleaning agents and asked curiously, "Why would the Leaky Cauldron have..."

Hanna's face flushed at once, and she stammered, "I asked Great-Granduncle too... He said it was because the Leaky Cauldron had been around for hundreds of years..."

"When Great-Granduncle took over the Leaky Cauldron back then... he bought a lot of magical cleaning agents... Unfortunately, the Leaky Cauldron was too old, so they ended up being useless..."

Neville nodded in sudden understanding. "Hundreds of years ago... That would be several fifty-year periods, so no wonder!"

Hearing this, Vizet and Luna exchanged a smile. They had discovered