I wouldn't pick Floatzel, and neither would I rely heavily on swift swim. The best way around Tailwind is to play defensively, in my opinion. Do you carry Protect on most of your Pokemon? Since Rain is an automatic and everlasting weather, as long as a Sand Stream, Drought, or Snow Warning Pokemon doesn't switch in, you really have the whole game to sweep with Swift Swim. Perhaps your best choice is to knock out the Tailwind user the turn it uses Tailwind, and then Protect and switch to wait until Tailwind runs out. If that doesn't work, you can also run a Pokemon with Trick Room or Thunder Wave on your team to make Tailwind either a hindrance or useless, respectively. The Trick Room option would only really work with at maximum two Pokemon with Swift Swim, though, because otherwise you'd be forced to not play Politoed in order to counter Tailwind.
Hopefully that helped, and you'll find some sort of solution in the future. It'd be nice to know what the rest of your team was for more accurate advice, but in general it seems that 85/55/50 defenses might be a shaky plan in a meta wrought with priority.
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