Simple, cheap, and effective: Hamburger mattenfilter. Basically you put a powerhead or airlift tube at one end of the tub and put a piece of filter foam vertically in front of it. I use the pond filter material that comes in 5' wide rolls; you can get enough for several tanks for about $20.
the best filter for small feeders are sponge filters because they do not suck in the feeders unlike other filters and they provide good biological filtration but the downside is it is not as effective in mechanical filtration