I tried a home therapeutic phlebotomy a few years ago.
I was desperate because my hgb was high, so the Red Cross wouldn't do it. Also, I was supposed to fly internationally in two weeks and had two Dr's telling me that flying would be dangerous. Unfortunately, for some reason my pcp was dragging her feet scheduling me to have it done at the hospital.
So, I bought tubing to fit on the base of an 18g hypodermic at the hardware store, and a paint bucket with volume marks.
I disinfected everything and had a friend insert the needle. I have video of the blood flowing into the bucket with us cheering! Then it stopped. He tried five more times, and the same thing happened.
A week later, I finally was phlebotomized at the hospital. It took over an hour, because my hgb combined with high natural clotting factors kept blocking the system. They use a saline backwash to clear the block.
I wore long sleeves because one of my arms looked like a heroin addicts arm.