Heres what ihave done and works well.
get a container of water (luke warm) large enough for the snake to fit in.
add a small amount of listerine (mouthwash) like a cap full to 10 litters of water put your snake in it for about 30mins
take him out rinse him off good with a wet cloth (preferably white) then you can see the mites coming off and sticking to the cloth.
while you are waiting for the snake to soak clean the cage with water and bleach at 30:1 (water:bleach)do not use this tank for a week keep the snake a rubbermaid or somthing easy to clean, because you will have to repeat cleaning the snake and container everyday for at least three days in a row.
after 3-4 more days clean snake and container again then put him back in his origional cage. then after another week i do another full clean.
This has worked 100% for me on 3 diffrent occasions.
Note: make sure your snake is not drowning, but also make sure he goes under water a few times as mites like the eye sockets and the chin folds.
also two sided tape wraped around the outside of the tank will ensure no new mites will get in and no old mites will get out to lay more eggs.