That reminds me of a reactor turned on it's side?
Depending on the pump you have, you might be better served running the water over the side, to the bottom of a bottle or cylinder with a diffuser plate at the bottom and letting the water make it's way back up the cylinder through the media to an outlet.
Take a look at the design of these reactors as an example:
They all employ the same basic concept, just different containers, etc.
When I was all SW in the fish room it really ticked me off that these things were initially made so huge just to hold about 1/2 cup of ferric oxide in suspension. I eventually made a second diffuser plate and glued it to the middle of the inlet tube so I could run carbon in the upper half. Worked like a charm.
Sticking with the DIY route I would bet that an acrylic spaghetti storage container would do the job. Either a screw-down jar with an O-ring or one of those snap-down types with the rubber seal should work perfect. I'm just thinking you'll have issues with the horizontal row of holes unless you mount it directly over the tank.
Man! You really got me thinking out loud there.