Some have drawstrings, I just leave mine open and hang the edge over the side so it doesn't fall in.. If you do tie it off, make sure there is enough space for the hops/grains to roll around inside
I bought a 5 gallon paint strainer bag from Home Depot. It has an elastic top that stretches over the rim of my stock pot and leaves plenty bag to almost fill the pot. Grains float/steep freely. When its time to remove the grain, I pull the elastic off the rim, and lift the bag and do the waiting game while the grains drain.
Mine is big enough to wrap around the top of my pot. There's enough left over to use two binder clips to hold it to the handle... That way my grains can float free.....
I use the paint strainers as well and tie to the handle on the pot. I think i will try stretching it over the pot next time so the grains will float freely.