In the very early pre-planning stages of considering ducks. Love the above ground yard timber ponds I've seen others post and will most likely go that route instead of trying to dig in the clay soil we have here in sunny San Diego. One plan I saw didn't have a filter, just a drain. Another is in the building process and they are putting a filter in a separate box. I am trying to determine how often the pond would need to be drained if it did versus did not have a filter and it was large (say 4'x8') and I only have two ducks (at the most 4). I want to use the duck water for our garden and because we are such a dry climate conserving water as much as we can is encouraged. Would a pond that size stay clean enough for twice a week emptying or would it need to be every other day? If I'm emptying it that often would I still need a filter? Or is the filter what allows the pond to stay relatively clear for every other day/twice a week emptying? Also, since I have such cruddy soil, grass in the run just would not survive for long. To prevent stinky mud puddles, is pea gravel or sand a good substrate?