Connecting Canister filters to built in overflow

[lastlight]

Ah cool. They are sealed that does make sense. I'd tee off one bulkhead and feed both filters if possible and then have the other as an emergency overflow. You won't have a siphon exactly but you should be able to still work it like a herbie setup and have some safety too (assuming 1 drain can handle the output of both filters (if not there'd be a bit of negative pressure on the filters which might still be ok?)