Turtlerama -Trickle Filters
I Followed these intructions, (kind of), which I was given by Mike E. (I'm never sure when you should post another person's name online). I post them here, as he knows what he is doing better than I.
"Yes I use trickle filters as often as possible. They are simple to make.
I start with a rubbermaid tote bin of appropriate size (usually as big as I can fit above the setup).
I then add two outlet fittings to one end. I use the plastic grey electrical conduit fittings, Can-tire or home dep., as they are cheap and you can get male and female so they fit together inside and outside. I use pvc cement to seal them. I put the main return about an inch from the bottom and the second about an inch or two from the top to act as an overflow.
For an intake fitting I use a 1/2 inch fluval elbow fitting threaded into a hole in the lid. I make all holes in plastic with a soldering iron to avoid cracking. The intake does not require sealing. I use an old spray bar from a canister filter and attach it to the elbow fitting on the inside of the lid.
This helps spray the intake water evenly over the filter media inside the bin. Half inch pvc pipe also works here if spray bar is not available (cheaper too).
Inside the bin I use a layer of lava rock a few inches deep. It has lots of surface area for beneficial nitrifying bacteria to grow and its cheap. I use the large stuff meant for bbqs. Can tire sells small bags of it very cheap. Keep the opening to the outlet clear of any lava rock. I use a layer of filter floss or foam above the lava rock. If using floss which is much cheaper then I place a plastic grate between the floss and the lava rock so the floss doesn't mix in. A section of an old undergravel filter works well for this.
I usually use multiple layers of floss and I put a mix of activated charcoal and zeolite in between to aid in aerating and absorbing ammonia.
A second plastic screen placed on top of the media can assist in the even distribution of water but is not critical.
This system is not water tight and the return works by gravity hence the name trickle filter. So it must be mounted above the tank. Supported and hidden inside a cabinet-canopy works well.
The only costly part of the filter is the pump. I use small garden submersible type pumps with a lift rating suitable for the job. I've also used power heads from submersible aquarium pumps like fluvals or power heads from under gravel filters.
This system provides both biological and chemical filtration on a scale more suitable for turtles than what a standard fish tank filter can provide. They are a breeze to clean (no o rings or clips) and its self priming. I change the floss as needed always keeping a piece of the old floss to help seed the new. About every 3 or 4 months I gently rinse off the lava rock using used aquarium water and I replace it once a year."