Zi Collection, Page Position: Lower. Radical: Wrap (bao). Kangxi Strokes: 8. Page Number: Page 151, Number 14.
According to the Tang Rhymes (Tangyun), the Collected Rhymes (Jiyun), and the Corrected Rhymes (Zhengyun), the pronunciation is derived from the characters tu and dao, sounding like tao.
Explaining Graphs and Analyzing Characters (Shuowen Jiezi) defines this as earthenware vessels. In ancient times, the Kunwu clan invented the production of these vessels. The character form is derived from the radical Jar (fou), using an abbreviated portion of the character for wrap (bao) as its phonetic component.
The Jade Chapters (Yupian) states that it is now written in the form pronounced tao.
Additionally, the Correct Character Mastery (Zhengzitong) notes the pronunciation is derived from the characters yu and shao, sounding like yao. It is the same as the character for kiln (yao). There are old kilns from the era of Emperor Wu of the Han Dynasty located on Mount Nanshan.