Just remember the larger the surface area inside the canister and the lid (bigger around and apposed to narrow and long) will require more strength. Even though the pressure is only about 9 PSI it will exert allot of force but remember we are talking relative here. In other words you cant use something as thin as a bucket with a sealing lid, you need something about 4 times thicker with a lid that has supports.
PVC would be more then strong enough but ABS is a bit on the fragile side and prone to chipping. If you can find 8" PVC with threads and caps at both ends that would be a good start.
But jmhart is right, having a screened void at the bottom for filters water collection, an exit fitting at the bottom to an external dry pump would be so simple to maintain, then all you need is a threaded top where you load the media with an entry port going through the top of the lid permanently sealed that hooks to a quick disconnect fitting outside.
