Old-style KILNS are still sometimes built up a long slope to assist in creating a constant draft (heat rises up the slope, inside the furnace) to generate the high heat needed to fire clay.「Wrap」is the outer layer of the kiln and a「crockery pot」is being fired within. DISCIPLINE and TRAINING are needed to keep the fires「burning hot continuously 24 hours a day」(which also connotes constant training), since if the fires weaken, the clay PORCELAIN objects inside will be ruined. The same folks who operated the kilns often were the artisans, representing education and skill, creating objects of ART and CULTURE.
Alternatively,「naked human backside with head tense for a long time wrapped in skin slit with horse cock head downward thrusting into cavity.」…these elements quite clearly represent a PORCELAIN DILDO, used by harem concubines and aristocratic Chinese females with CULTURE, years of DISCIPLINED TRAINING in sexual and other cultural arts, and HIGH-CLASS BREEDING, to PLEASURE themselves and their partners:「Historians do not know who invented the dildo but most believe that dildos most likely originated in Asia. Dildos have been found in China that date back as early as the New Stone Age, that's more than 12,000 years ago and most recently a tomb was uncovered from the Han Dynasty in Xian, China that was home to a rather interesting collection of dildos. Seven cast bronze dildos were discovered and evidence indicates that they were used by palace maids on sexually deprived imperial concubines or aristocratic women during the Han Dynasty. Also discovered in ancient China, are handcrafted dildos which double as works of art…」
[ link to text and images is now dead, unsurprisingly, but was https://chinahub.blogspot.jp/2009/02/ancient-chinese-dildo.html 2012-09-11 try your own Internet search instead ]…no shame there, it seems. Note that PORCELAIN literally means「vulva of a sow, female pig.」

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: pottery; pleased
Japanese EDRDG: pottery, porcelain
Unihan extended: pottery, ceramics

Used within names (nanori)
す　･　すえ