It takes quite a bit of pressure.
I " milk" from the back of the pec fins, with my palm under the belly, applying pressure with the thumb and forefinger just below the lateral line.
Kinda like squeezing the meat out of a bananner
The fish must be 150%, totally slap azz knocked ,out via clove oil or 222.
Not just dreary, like I do to inject, or scrape. Damn near dead...as to response to stimulii.
Bigger koi ( over 25 inch) almost "dump them" if it's fully gravid gal, but not holding eggs for a long period of time. After time it gets much more difficult.
I tried to do one of Koiphenators Shiro Utsuri and was followed up , a month or so later, by Al Riggs dVm ( good one), who also tried, and then injected her with pituitary hormone, to no avail.. It had been too long and the mass was solidified. I THINK the fish was finally lost to egg binding..
I have a couple of Sarassa that need it in the next few days.. normally they would let loose, but the holding tank is a bit overstocked and they just wont..
I could set them up in a 400 gallon, with a couple of males and some shade cloth, or mop heads, but this is only a 10 minute procedure.I'll "milk them"
If my guy shows up

I'll do a few pictures of the procedure.
Waddy has some pics of the procedure , on his site.. with larger fish.
As to re-absorbtion.. A gal can do it in a 4 season climate, fairly quick, from what I understand... never seen it.. hear / say.
Matt or JR or ona them yankees ( even Brady, in his fairly mild climate) could elaborate.