I have not used the screw type, but I have driven 2 inch pipe into the lake bottom. What I found was that you need to anchor the dock to a seawall or it shakes alot.
When I redid the dock, I used 5 gallon buckets filled half full of concrete. On our lake the buckets sink about 3/4 of the way into the muck. The water is about 5 feet deep.
You jet with a water pump. Typically a two, three, or four inch gas powered water pump is what would be used. Just drop the suction side hose in the lake, connect the output hose to the pipe you want jetted in and go to work.
also, drill you holes for thru bolts, before concrete, as concrete gets to the holes, insert the bolt. besure to coat the bolt in grease, or some other protection. use a small pea gravel concrete mix, easier to get packed.
