Raising this thread from the dead rather than starting my own, because it's essentially the same topic.
I've been doing BIAB partial mashes, I think I've done four of them now. For the first three, my process was:
Mash in my 5gal kettle, pull the bag and drain in a colander over the kettle for a while, then transfer the bag to a big bowl to sit. Pour the wort into a 2gal pot to store (with overflow in a second pot if needed). Heat sparge water in the 5 gal pot, then dunk sparge, and then pour everything back into the 5 gal pot and start the boil.
This had two huge problems. The first is that it's a lot of pouring hot wort back and forth, which is labor-intensive and dangerous. Second, it takes a long time to heat the water, and because of the wort-dance, I can't start heating the sparge water until the mash is over. This means the grain sits for a long time, cooling off, and makes it really hard to hit the sparge temp.
This time around, I decided to scratch the dunk sparge and just do a fake fly sparge / grain rinse. I heated my sparge water in a couple of smaller pots while the mash was wrapping up, and then moved the grain bag into my heavy colander and set it on top of the kettle. I used a pyrex measuring cup (because it was handy, anything would have worked) and sprinkled the sparge water over the grain. At the end, I had to have my wife to the last bit because the kettle filled up to the point that it was hitting the colander so I had to lift it out to keep things from overflowing.
It seems to have worked as a fine substitute for my previous process. My efficiency was at least as high as before (not great, 60% or so), and may have been 65 or 70% (depending on my as-yet-uncalculated trub losses). The big thing is it eliminates the above problems, and if I back off on the volumes a little bit, I wouldn't have to do the colander lift.
So I think I'll be doing it this way for a while.