Was from my grandmother's family on the east coast (farm family in Hudson Valley/Catskill area of NY State)
Stamped "Edwin M. Knowles" - See Image. The Edwin M. Knowles China Company was founded by Edwin Knowles (another of Isaac's sons) in 1900. The piece is a slop jar, not a chamber pot, but is indeed part of a toilet set. Companies like E.M.Knowles discontinued the manufacture of toilet sets as more and more people got homes with running water, so it's reasonably safe to assume this ware dates from 1900 to no later than World War I.
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