At first I'd just put it in a colander in another pot, squeeze it by putting a plate on top (it's hot). Then I'd pour hot water over. Last time I "dunk sparged" it in another 3.5gallons, stirring some. I actually think the first method was better, but I can't be sure. Even though that's 7 gallons, remember that the grain soaks up some, then some boils off, then some is lost to hot break, cold break and hop trub. The dunk sparge needs to big pots. The other can be done with your 5g and a big pasta pot. The colander should fit inside the pot if possible, or the wort will spill over the sides when squeezed. Many people practice no sparge BIAB with full volume, but many use the methods I've described. Check the BIAB sub-forum for more tips.