While being under influence I'd say drink plenty of water; keep it up the 1-3 days afterwards as well just to make sure you flush your bladder properly. Cranberry juice is good for your bladder so that is a possibility. I believe vitamin C is as well, and extra vitamin C won't harm.
Don't use enough to gain a proper tolerance; so twice a month at most of less would be good. Taking more risks getting a tolerance, and getting a tolerance makes it much more nasty for your bladder as more nor-ketamine will pass through it. If you already abused the substance and have a proper tolerance, grapefruit juice dóes work; it lowers the needed dose by about half for me and doubles the duration of effects. I noticed no unpleasant side effects from doing this other then it lasting longer so if you plan on sleeping afterwards its good to take the extra duration in account. This way you need less, so less has to be metabolised, which I assume is healthier on your organs.
Still its best to avoid that situation to start with by limiting use to 1-2 times a month. A recent study also claimed there were no mental impairments in the user group that does it 1-2 times a month, while the daily use group did show some impairment (ex-users however did not, suggesting any problems mentally are of a temporarely nature).
I have no clue which of this count for methoxetamine too, I wrote it all for ketamine, but I'd say treat it the same but with even more care as its new and barely researched, of ketamine we knów the risks; worse short term/ word memory and bladder issues; with methoxetamine we really have very little idea if any.