That's why having a BIAB bag with handles sewn on it is really nice. I brew on my back porch so I screwed a stainless eye-bolt into the joist above so I can rig up a rope and pulley. I just take a big carabiner and clip all the handles together and then haul out the bag. I took a plastic bucket and drilled a bunch of holes in the bottom which I place inside a 2nd bucket and then lower the bag into that to drain.
If you can get handles sewn into your bag that would be a good option, otherwise I would use the millers knot or just make a loop of rope and use a cinch knot around the gathered top of the bag.
Brewing Soon: Scottish 80/- with Cascade and Willamette Hops Double batch with a "IPA" mode out of half with added hop tea and dry hops.
Bottled:Pumpkin Ale & Mcquaker's Chocolate Oatmeal Stout
Drinking: Above & HUB IPA & Dechutes Black Butte Porter