The bottle to serve hot Sake is called Tokkuri (徳利), that is used like a teapot. From the Tokkuri bottle, hot Sake is poured into a tiny cup called Choko (猪口) or O-choto to be drunk little by little. There are various shapes and designs for Tokkuri, but it usually contains 180ml or so in accordance with the unit Gou 合 . The Gou is a traditional Japanese unit to measure quantities, which is still used for many things, Sake, Miso paste, Soy source, beans and even rice.
There are actually several traditional Japanese units that still exist and are used often in daily life. They are sometimes used in business too, so it is useful to know of them.
Numbers in Japanese
1(ichi) , 2(ni), 3(san), 4(yon), 5(go), 6(roku), 7(nana), 8(hachi), 9(kyu), 10(jyu)
11(ju-ichi), 21(niju-ichi), 31(sanju-ichi), 41(yonju-ichi), 51(goju-ichi), 61(rokuju-ichi)
71(nanaju-ichi), 81(hachiju-ichi), 91(kyuju-ichi), 100(hyaku)