I tried looking back at threads, but I have a pond that is about full, and I have a hollowed out tree....big enough for large bass to swim through.

Would like to add this in the pond, hopefully to give the big pass a place to hang out....but how do I sink it?

Tree trunk is 8-10 feet long and hollow part is 20 inches in diameter. I can upload a picture tomorrow.

Or am I just wasting my time on this structure. Not worried about tannins, tree had been dead for sometime, no bark, was not oak and I’m already treating pond with muck pellets and activated charcoal because of the leaves falling in.

Not sure why the photos are turned sideways.

Use a boat, float it in place, add weight from the boat to sink it.

This sounds like it could be quite an adventure! Surely that will require video documentation when the actual day arrives.

Ditto on the boat and weights. I'm thinking multiple cinder blocks tied together in pairs with nylon rope and draped over the top of the log. Keep adding pairs of blocks until it's sunk.

Bring more cinder blocks than you think you'll really need.

Folks generally frown on my approach, but I just let larger logs float till they lodge somewhere. If I don't like that location, I shove them off again and see where they land. Alternatively, I leave one end lodged on the bank where I want the log. The logs do sometimes move again during high water. Eventually, they sink or rot.

If hollow, run a piece of wire through it and attach cinder/cement blocks

I added pictures, just run wire through log and through 4-5 cinder blocks on the bottoms?

How long will that wire last in the water?

Probably longer than the log will depending on wood type

Get a bag oh concrete inside it and roll it down the bank when dry?

Run a nylon rope through the hollow and tie the loose end back onto the rope.
Leave enough length on the tag end to tie off on a bank anchor of some sort.
Push the log into the water close to where you want it to end up.
If it sinks, cut the loop in the rope and pull it out.
If it floats, tie it off to a bank anchor.
It will, eventually, absorb enough water to lose bouyancy and sink.
You can then remove the rope.