Sitz Bath

bathtub in which one bathes in a seated position; therapeutic bath taken in a sitz bath (often used to treat hemorrhoids)

For hydrotherapy in dogs, see Canine hydrotherapy. Hydrotherapy, formerly called hydropathy involves the use of water for soothing pains and treating diseases.Its use has been recorded in ancient Egyptian, Greek and Roman civilizations. Egyptian royalty bathed with essential oils and flowers, while Romans had communal public baths for their citizens. It has been long accepted that hot water springs can improve health by increasing circulation.  Hippocrates prescribed bathing in spring water for sickness. A Dominican monk, Sebastian Kneipp, again revived it during the 19th century. His book My Water Cure in 1886 was published and translated into many languages.
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A sitz bath is a type of bath in which only the hips and buttocks are soaked in water or saline solution. [more]Sitz bath - Community and Resources

Noun
1. a bathtub in which your buttocks and hips are immersed as if you were sitting in a chair and you bathe in a sitting position
(synonym) hip bath
(hypernym) bathtub, bathing tub, bath, tub

A tub in which one bathes in a sitting posture; also, a bath so taken; a hip bath.