If you insert the STERILIZED needle in the right place it shouldn’t hurt at all.
You want to go from the edge sideways and parallel to the rest of the skin (instead of straight down) and then through to the other side. This gives you two small punctures so you can squeeze the fluid out.
Then cover with a sterile bandage. This is important because you want to avoid infection.
When it fills up again is when it will be painful again so just keep squeezing out fluid whenever necessary.
Whatever you do, DO NOT remove the skin. This is what’s protecting the new skin forming underneath as well as keeping out infection.
In a few days, it should stop refilling with fluid so just leave it alone until the old skin falls off on it’d own.
I usually didn’t do the fluid draining during the day when I was walking on it but rather at night as often as needed and especially just before falling asleep.
The main reason I chose to do the piercing and draining is because most of the pain from a blister is the pressure exerted by all that fluid. When you drain it , it lessens the pain. You just need to be careful and meticulous to avoid infection.