The most common and most likely answer to this crossword clue is the 10 letter word SHAMPOOING
I've seen this crossword clue in The Guardian
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More clues leading to the result SHAMPOOING
Buddy explains!

The straight part
We know that "Using bathroom product" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case using bathroom product = shampooing.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SHAMPOOING mean?
SHAMPOOING verb- To wash one's own hair with shampoo.
- To wash (i.e. the hair, carpet, etc.) with shampoo.
- To press or knead the whole surface of the body of (a person), and at the same time to stretch the limbs and joints, in connection with the hot bath.
- The act of cleaning something with shampoo.