You want it on the outflow, not the intake. On the intake side, the CO2
will go straight into the filter. You may as well skip the gravel vac tube
if you're going that route.

wrote in message
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I want to splice a gravel vac tube into the intake line of my Eheim 2328
canister filter and bubble CO2 into it. Anyone see any problems with this
or have any tips?