I have done San Pedro a bunch of times. I cannot stand the aromatic solvents like xylene or tolulene, so I opted for a method called the "triple steep". You can pretty much figure out what it is, but I'll explain how I do it, and why I do some of the things I do.
First I skin it. The skin and the core are worthless so why add to the volume you are working with? I cut in between the ribs all the way to the core in lengthwise slices. Then I pull each rib off of the core with my finger and toss out the core. Next, I use a great peeler I got at a gourmet kitchen store. Tried the run of the mill peeler you get at the grocery, but the expensive one works best. You only want to cut off the very thin waxy skin. The dark green slimy inner skin just inderneath is where most of the mescaline is. Expect this to be time consuming. I will prepare any number of cactus, but you peel your own. After each rib is peeled, I cut into cubes and run through a juicer into 300 ml of tap water. Set aside the juice and retain all of the slime and pulp, which I add 300 ml tap water to and I steep the pulp and water for about 20 minutesonce the water begins to boil. I repeat the 20 minute steeping interval 3 seperate times, straining out the pulp and adding more water. The total collection is 300+ ml cactus juice and water + 900 ml cactus tea. I compost the pulp and boil down the 1200 ml. This is where it can get slimy. The slime is called a protein break. By heating and stirring constantly, you can get the protein to break in the first 20 min. Try to add a 1/4 tsp of table salt
(no more than that) if you can't get the protein to break after 30 minutes of heated stirring.
I usually like to make the doses a half cup in volume so they go down quick. Or if I am making 4+ doses I like to reduce the total volume to 2 cups and add 2 cups cold water to it with a pack of lime jello. Then you can measure them into disposable cups. This works better if you really, really, really filter the cactus juice. If not it leaves a thick green scum on the bottom of the jello shot. I always vacuum filter the cactus reduction and refrigerate. Then make the jello with hot water and cold cactus juice.
I toughed it down the first time, and kept it down, but was nauseated and uncomfortable for the whole trip Which have all lasted about 22 hours, btw consistently. So now I always only deal with the nausea until I feel the trip coming on strong and then I get that stuff out of me. It is gross but more comfortable in the long run. Long lasting trips. Wave after wave of peak after peak. exhausting. The only thing that could be better is if the visuals were a lot stronger.