I am about to infuse my mango blonde ale with 13oz of hibiscus. I don’t want the sack to float I think it would be better if it floated about mid carboy.
I am thinking about marbles or maybe a heavy stainless steel lug nut or something but I am afraid of how they would chemically react with the fermenting beer.
I use a large ceramic soup bowl in a 5 gal bucket to dry hop. I wrap the hops and the bowl in cheesecloth and lower it all in. It took me a while to find a bowl heavy enough, but it works great.
Based on my experience dry hopping with hops in a bag, weighing it down isn’t necessary. I don’t know why people work so hard at something that makes so little difference.
Ditch the sack and rack onto pellets in the secondary. They float. Cold crash it and they sink. Top, bottom and everything in between - all bases covered.