Yes, true good trash pumps around here start at $1,000, and that's used. I don't know if I would fret over trash v semi-trash. If you need to remove that much sediment, it would be better to just hire someone to clean it out with the proper equipment. With a semi -trash you could stir up the water and mix sediment in and it would pull it out, especially a 4". But even doing that is time consuming, I wouldn't want to do quantities of that. My experience too is that the suction hose has to stay under water, and it needs to remain short as possible(most are 20' or less). Its a big hassle moving that around as needed. I think the big problem would be gravel. Depending on the pond bottom and how good the pump blades are to take the impacts.
I suppose if you could pick the lowest spot, leave some water in the pond, and walk around and stir it up, pushing the sediment towards the one spot as the pump works, it may work over several go-arounds. Maybe do it after each rainfall? The discharge hose will fill with the heavier sediments too, especially if it goes uphill or in low spots.
Where would you push all this sediment and how far?
