Hi,
If you need something that will pump that much water as well as provide a waterfall, then you will most likely need an outdoor-like pond pump and filter canister. Basically, you buy two separate units (one being the pump and the other being the canister filter). You can make a wooden box stand to slide the canister into for mounting. The pump will need an electrical connection that I would strongly recommend be connected to a GFI (Ground Fault Interruptor). When it is set up, you will have the pump running one line to the filter, and the filter will have one line running to the source of your waterfall. Your waterfall will be the return for the water. I have a "Little Giant" pond pump that I bought from Lowes that really wasn't that expensive. The canister filter is about $40.00 filter pads.
Hope this helps and if you have any more questions, feel free to post them here or contact me directly via the link at the top. I might be able to provide you with some links to decent and cost-effective products.
Best Wishes,
Chris
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Chris Law
U.A.P.P.E.A.L. (Uniting a Proactive Primate and Exotic Animal League)
Herpetoculture Element Representative