Do you know what I do for a living? I clean spit out of tubas.
There's PLENTY of work: ALWAYS (without spending most of one's time cleaning spit out of tubas).
A considerable percentage of the time - when people travel (probably mistakenly of the belief that - simply because bloke is a tuba player - bloke will repair their tuba better than their local guy) - and they specific things for me to do - what they need done - MORE than any of the things that they brought in their instruments to have done - is to have nasty slime and hard scale (lime, etc.) removed from the interiors of their instruments.
This stuff reduces the capillary and valveset bore size, causes valves to stick (with people then spending serious money on all sorts of - "marvelous/mysterious" oils), prompts people to always depress valves or valve levers when removing slides (as the vacuum effect sucks hidden crud from knuckles and porting onto the valve casing surfaces - resulting in even worse valve-sticking), and other related issues.
Oil does NOT keep a tuba or euphonium absolutely clean, but GENEROUS DAILY oiling greatly discourages that mess from clinging to instruments' interiors.
Additionally, cheap (and I mean REALLY cheap) oil is a way to financially enable oneself to keep up with this regimen. I have not cleaned any of my instruments in several years (other than - possibly - a "cheater/b.s." cleaning - whereby I jetted hot water through - perhaps - one of those instruments' valves (main slide removed) and wiggled the valves a bunch.
Also - if you can find someone with the willingness and ability to *"blueprint" your slides (assuming having this done is financially viable, which - and I understand - it isn't always), you can use the same oil on your slides that you use on your valves - which will prevent very thick oil or grease from migrating from your slides to your valves, gumming up your valve oil, and then (as I see often posted) probably (??) incorrectly believing that "when I use blah-blah oil, it gums up my valves".
Taking a tuba all the way apart (particularly rotary) submerging it in a tank, pulling it back out (big long black rubber gloves) emptying all that chemical back into a tank, rinsing out the remaining chemical, and following up with (all over the tuba) some hand-cleaning ...This is a thankless (may I use the adjective, "gross"?) job. It would be more pleasant to encounter MORE instruments that don't really need this job, simply do repair/maintenance/customization work that is desired by instrument owners, and then - this... - repair MORE instruments, make just as much money, and (again) spend LESS time doing "gross" stuff. ...plus: All of those cleaner instruments will be performing better for their owners - without paying a bunch of dough to have them cleaned.
also (and important) "giving my instrument a good bath" (in a bathtub - along with some sort of detergent) isn't actually very productive at all.
finally: "Rotary tubas' valves really don't need to be oiled all that much." ...sure...yeah...right...you bet...um-hum...
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*perfectly align all of the slides...with (though all of them being aligned) perfectly a few of them fitting just as well as pistons fit into casings, but perhaps only those select few whereby this would be beneficial