Lube filter's o-ring.

eheim uses Vaseline

My Eheim filters came with vaseline to lube the rubber. Same as the stuff in the drugstore, just smaller, more expensive tubes.
 
Most of the online pet places have silicone grease. Just do a search on silicone grease on Thatpetplace.com or Big Als's. Not hard to find.

Jim
 
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