Best way to siphon debris on the bottom of 3-4' pond?? and pond filter ques:

The Diatom filter would be good for a quick clarification of the water. I would go with a regular gravel vac type apparatus for the pond, unless you want to fill it with the same thing, and then a Python would be a good option.

Welcome to AC!

~Matthew

If possible, empty it and use a 'wet/dry vacuum' on it...

I don't have a bottom drain either, however I have a very strong pump that can get most of the gunk from the bottom. when I designed my pond, I intentionally made one area deeper than all the others. 90% of the debris settles in this area if it doen't get pulled up by the pump. since it's all in one area, i can then use a pool net that I picked up new from the pool supply place. it's the same type of netting that a skimmer would use (fine netting), but it has more of a basket type of net that can hold the debris. the little bit of settiment gets taken care of by the pump/filter.

there are powered vacuums out there designed for pond use, but I find them to be very expensive. as joe mentioned, a wet/dry vacuum can do the job, prefferably one that is new and hasn't been used outside of the pond environment. and if it has an air filter (heppa or otherwise) remove it. the downside is that you have to work quick with a small body of water like that, the vacuum can drain the pond quickly. of course, a new pool vacuum would be better, since it already has some useful 'nozzles' (for lack of a better word) that would ease in sweeping the bottom of the pond. after all that, I still reccomend the manual approach of using a net.

as for pumps and filters....

the Little Giant pumps are a pretty good line of submersables. the sponge filter that comes with them though, is complete junk. I used to have a gravity fed filter made by TetraPond. it was rated for ~600 gallons I believe, and sat above the waterline for easy maintanence. it worked great for what it was, but still required a lot of upkeep. optimally, an inline pump and filter approach is your best bet, but with the size of your pond, it's almost overkill.

your existing pump and a gravity filter simmilar to teraponds models should be adequate. use the existing filter as a pre-filter to remove the bulk of the debris before passing through the system. then the filter won't (read:shouldn't) need as much upkeep.