My wife and I had a small sponge filter in our ten gallon betta tank. The filter did a great job. But all the crud just wound up back in the tank whenever I removed the filter to rinse it.
We tried other filters that were easier to clean. But anything small enough for the tank would clog too quickly. And anything with sufficient capacity created too much current.
So I hit upon an idea. And a trip to Petsmart provided the raw materials.
This is a Marina brand HOB
breeding tank. It uses a simple air-powered siphon to lift tank water into the box and an overflow chute to return it. All I did was add a baffle to force the water to flow down through the gravel on the right and back up through the poly-fill on the left.
I can't really call this a DIY since it's just a tweak of an off-the-shelf product. And since I just finished it I don't know how well it works yet. I'll post an update in a few days after I see how it works.