The most common and most likely answer to this crossword clue is the 8 letter word FOOTBATH
I've seen this crossword clue in The Guardian
F
O
O
T
B
A
T
H
More clues leading to the result FOOTBATH
Buddy explains!
The straight part
We know that "dog-washing device" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dog-washing device = footbath.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 FOOTBATH mean?
FOOTBATH noun- The act of soaking or washing the feet.
- A small basin or bath designed for soaking or washing the feet.
- A liquid mixture, often medicinal, for soaking or washing the feet with.