Elements of「rod in meat」have various possible interpretations: some sort of sexual activity by insertion of a rod-like tool into a meat orifice, reaming a urethra with a bougie, or perhaps as a reference to the bone present in the penis and clitoris of nearly all mammalian species (not humans, in case you are searching for yours). This bone, the baculum in males and baubellum in females, enables the individual animal to be ALWAYS READY, PREPARED for immediate sexual coitus in the event an opportunity presents itself, without the need to wait for sexual arousal and therefore not to miss one's chance to be the first-in, first-out. Other interpretations likely are self-explanatory to mean BE PREPARED.
NOW IN USE, or the EMPLOYMENT, HIRING OF SERVICES, USEFULNESS.「Meat, mooning」with a「rod, reciprocating motion」within, DOING ONE'S BUSINESS with service providers, or by oneself.「Mooning buttocks in vertical motions」is suggestive of both twerking, selfies, and twerking whilst performing a selfie…not to mention HIRING OF SERVICES, USEFULNESS for attracting a client, a series of clients, or a large group of clients by a service provider.
Scatological references are listed for only Japanese meanings, but that doesn't preclude there were none in China:「mooning buttocks」with「vertical motion」also describes DOING ONE'S BUSINESS while EXCRETING, DEFECATING, performance of a FUNDAMENTAL TASK, SOMETHING ONE MUST DO, oft-repeated, noting that the vertical motion in this case is that of down, into the soil. Same meanings apply to a「rod in meat」used as an element referring to the use of dildoes in one or both orifices by, together with, or in females preparing for intercourse (or, not…see 荽).
Chinese meanings include to EAT OR DRINK such as while partying, EXPENSES such as the entrance fee or other purchases of services and food, USEFULNESS to indicate that entry was needed or desired to satisfy a want. Dumping one's urine and feces as a natural consequence as various concepts of EXCRETION.
Perhaps two「mooning positions」side by side (朋) as with the glyph meaning「gateway」(門), but the gates are now closed with the two internal sides juxtaposed, joined, and NOW IN USE with one another engaging in tribadism, female-female frottage. Indicating someone is NOW USING, EMPLOYING the services that are IN BUSINESS within as SOMETHING ONE MUST DO, an oft-repeated TASK:「on average, female bonobos engage in genital-genital rubbing about once every two hours」
[ https://books.google.co.jp/books?id=tz9mSyTWh0oC page 88. 2020-05-09 ]
Note the Japanese pronunciations coincide with meanings of both 'hot sticky white gooey splat' of pounded mochi and of 'precious treasure' (a personal dildo, perhaps, from a day and age when every woman, and some men, used a dildo).

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: to use; to employ; to have to; to eat or drink; expense or outlay; usefulness; hence; therefore
Japanese EDRDG: utilize, business, service, use, employ
Unihan extended: use, employ, apply, operate; use

Used within names (nanori)
たから