I think every one using different method of degrafting/rooting which you believe it is the best.
I break off a scion from the root stock and dry by using garden-lime.
After dried, washing off garden-lime completely.
I use rooting hormone (Gel) after completely dry (from washing).
There is a rooting hormone specialized for cacti overseas but we can not get it in here.
I keep the scion on a top of black empty pot until some roots coming out, showing as below.
As shown below, roots coming out, now you can put it on rooting medium ( I use shifted clay base cat litter.).
I think the rooting gel assists for rooting a bit.