Warm water works as it tricks the bot eggs into thinking the horse is licking them (ever wonder why they don't wash off in a cold rain?).
You have to be quick, however.
Keep a bucket of warm water beside you, soak a wash cloth, hold it against the bot eggs for a few seconds, as soon as you remove the wash cloth, immediately
start scraping the eggs and they should literally slide right off the horse.
For really hard to reach or sensitive areas (I am finding bot eggs on the sides of their sheaths this year
, Put some sort of ointment on them to smother them.
It can be anything from antibiotic ointment to hemorrhoid ointment. Leave it go for a day and they should come off fairly easy the next day.
Don't forget to pull jowel hair back and check for eggs along the jaw bones and underneath.
Those are migrating bot eggs and are laid by "Throat Bot Flies". Yes, they really do migrate into the horse's mouth by themselves.
Google "throat bot flies" and you'll get a few credible hits.
Hope this helps