Making it sink and keeping it sunk in one place are different weights. Due to water motio and currents it will take about 25 lbs to keep it exactly where you sink it.
I have learned this the hard way sinking PVC around my dock. Everything is buoyant to some degree to figure at least 30% more weight than it would normally just to sink it. To keep it in one place figure about 5 times that.

Considering that most PVC pipe is used to carry human waste do we want to assume its full when its caped?

Here is what I came up with ,

4 ft by 4 inch cylinder is .32 cubic feet.

a cubic ft of water is around 62 lbs , x .32 =19.8 lb

So I will be using 40 lb or more to anchor.

thanks for all the replies

MO

1 PSI equals 27.7 inches of water column. So at 16’ you’re looking at around 7psi.

Are we using "new" or "old" math?

I looked that up also ,, sch 40 pipe will not be required. The thin wall stuff should hold up fine.


Mo

This is similar to what I am visualizing. Capped at the top to trap air , maybe longer horizontal pieces ,

From my standing timer days , on my lake , 12 to 16 ft holds the most fish. So I would sink this in 30 ft
with the structure suspended with all the " limbs " at 12 to 16.

wish me luck

Mo

There is 30' of water in front of by boat house cuz.....plenty of room too.
You could sink a whole passel of them. I would not mind a bit.

How are you going to trap the air?

Why not pour an 80lb. bag of concrete in the bottom and cap it? Let it dry and sink it.