I've had a Marineland C-360 for years inline with an 18w UV though the outtake. Never had any issue as the sterilizer always had water in the viewing glass. it's still mounted horizontally on my stand. I have a FX5 now. Haven't had a chance to hook it to the UV yet, but should be no problem. I believe with the purge, both vertical tubes will have 50-60% water remaining in both lines. Of course, it depends on how long they are. Mine does when I shut the FX5 off, since I changed the tubes to clear vinyl. Due to it needing to clear a 42"H stand + 26" tall tank.
