Perhaps a better explanation of what you want/are doing would help.
I gather your talking about building a canister filter from PVC like midnight 's for example. How often it gets clean is a matter of diameter and not length as the filter material will clog faster with a narrow pipe. I suggest at least 6" diameter and & 12'- 16" long with a cap on one end and a screw cap on the other (where filter mat. is). these have worked for me on some specialty tanks.
Just stop the pump. (if it's an aquarium pump). Unless it's made from a balloon, the pressure won't matter.
It does depend on what type of pump you have as to whether you can push or pull water thru a filter tho.
Dr Joe
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