Actually one of the best things for fleas (outside of oral medications) is Dawn, no jokes. We had a bad outbreak after the dog brought them in and they got on our 3 cats so it was a battle of attrition as wed wipe out the infestation in one animals and it get reestablished on the others but bathing and flea combing them every day (and dusting the carpets and furniture with diatomaceous earth) eventually we wore them down, broke their lines, crushed their flea men and heard the lamentations of their flea women, who were then also crushed.

I still have PTSD flashbacks like 3yrs later when I feel a tingle on my leg and think it's a flea 😅