1) Are you using a weldless fitting kit, or DIY'ing it? I went the DIY route, and re-used the rubber o-ring and plastic washer that kinda fits over/around it to create the seal where the 1/2" nipple goes through the hole, and haven't had any leakage. You'll wanna make sure whatever fitting you put on the inside of the nipple clamps that O-ring and washer down good n' tight; I ended up having to add a couple exceedingly short slices of PVC as spacers.
2) Like, just the bag, no stainless braid or bazooka tube or anything? That probably won't work – you'll end up with the bag right up against whatever fitting's on the inside side of the nipple, with all your runnings (and grains!) trying to squeeze through a 1/2" max diameter hole... you'll get a stuck sparge almost immediately. Unless you're somehow holding the bottom of the bag up above the level of the spigot (holy dead space, batman!), you're gonna need something rigid with holes in it to create a larger surface through which your runnings can escape the grain.
