1/4 cup. Put warm water into your sitz bath until it's about 1/3 of the way full. Add 1/4 cup of epsom salt. Then add yourself. Hope it helps!
No salt. When I recommend sitz bath for my patients (eg after anal fistula surgery) I ask them not to add anything to the water. This is just based on my experience and other surgeons may disagree with this and may have different opinions.
I had fistula repair surgery a week ago. Wound was left open to heal, no stitches. Are sitz baths with epsom salt advantageous, promote healing?
Won't help or hurt. Since you are a male who had fistula surgery, I am assuming it was an anal fistula. Using epsom salts in addition to soaking in a warm bathtub has not been proven to help or harm healing. Just getting into the tub for 10 minutes or more at least 3x/day helps relieve pain, keep the area clean, and promote healing. If you think it helps, go ahead and use it! Good luck with your healing!
OK but not needed. Sitz baths help keep the wound clean and relieve some of the rectal spasm. Epsom salts does not aide either of those functions, but does not do any harm.