IMHO the sunsun is a very decent and well thought out in-line basket canister for a clone. It has O-rings where they are needed and the baskets rims and basket flow in-flow pipe overlap from the motor head to the bottom by 1/2" to prevent bypass. Much better anti-bypass integrity then my Fluval 404 which actually has weep holes and gaps in the baskets to allow bypass.
The thing to remember and as mentioned in my review thread is to use a Q-tip with Vaseline to lubricate all the O-rings, the internal valve gates and swivels, the hose fittings that screw onto the hoses, and the basket rims. This so that they will work easier, seal better, last longer, and prevent the possibility of a forced break due to rough handling, never force a part if it is stiff always work it back and forth until if gives then clean and lubricate before next assembly.
When placing your media inside you will have to learn what works best for you but as a general rule I try and keep the top and bottom basket with porous media rings or carbon so that water flow at the two most critical ends has a chance to accumulate enter and exit the canister.
The center basket is where I place my polishing media starting with a cut-to-fit piece of blue bonded pad against the grate to prevent clogging and provide some rigidity against the bottom basket grate. Stacked on top of the blue bonded pad (2nd layer) I place and fill the basket with hand plucked and puffed Poly-wool instead of Poly-batten so that it (the Poly-wool) will filter effectively through and though without matting too early with heavy dirt on the surface only like Poly-batten has a tendency to do in baskets. Finally I finish off with a third layer of cut-to-fit blue bonded pad and compress the springy sandwich I have made with the top basket.
Your not really compressing that much Poly-wool between the two Blue bonded pads in the canter basket, just enough to prevent flapper bypass when water flow comes up from the bottom of each basket grate and tries to lift-float the media up and and out of the way to bypass to the next basket above (an inharent problem with all top motor in-line basket filters). If the water were traveling in the opposite direction down and pinning the media against the grates like in the FX5, this would not be a concern. Of course heavy rings and carbon are not an issue, only those baskets filled with lightweight media but especially those with only one pad inside that can be easily lifted and folded out of the way when water pressure lifts the pad off the grate from the bottom-up.
So if you do that and keep an eye on flow every water change as an indicator of early clogging and needed cleaning, this filter should provide very good filtration and certinly every bit as good as any of the big name brand inline basket canister filters, circumference style filters excluded of course.
