I think it was in the BIAB forum where a guy had a nice post about how to prevent the bag from being sucked into the drain port. I haven't tried it yet, but it looks like a fantastic approach that should result in an equipment loss of near zero.
Edit: Found a link:
https://www.homebrewtalk.com/showthread.php?t=632544
Basically, prior to draining first and second runnings, he pulls the end of the bag on the side with the drain to the other side of the cooler and clips it to the cooler handle to hold it there. The does two things:
First, it prevents the bag from getting sucked into the drain port.
Second, it squeezes out the extra liquid in the grain (like a BIAB "bag squeeze").
I have a bag on order and I'm going to try this with my next batch.
My planned procedure:
Mash as usual using a bag in a rectangular cooler
Pull bag from drain side of cooler to other side.
Vorlauf and drain first runnings
Return bag to original position and add sparge water
Pull bag to far side of cooler again, vorlauf and drain second runnings
I think I can also tilt to the cooler to drain pretty much every drop out too.
I've been running about 61% brewhouse efficiency pretty consistently. I'm going to go with a finer crush and I'm expecting something close to a 10% increase in efficiency.