how do you clear out bounced contacts without hurting sender reputation

look at why they bounced too. a sudden pile of hard bounces from one import usually means an old or bought list, and spam traps tend to come with those. run any list older than a year through a verification service before you mail it, it's cheap compared to a reputation hit.

removing them doesn't hurt you, keeping them does. mailing hard bounces over and over is what damages reputation. hard bounces: suppress straight away. soft bounces: give them a few sends and suppress if they keep failing. and suppress rather than delete, otherwise someone re-imports an old list and they're all back.