Ah, don't ya hate that... a crash after nearly completing a long post. I can relate Pete!
Ok, sorry, my instructions are not based around an urn, so I see now how it gets confusing and ambiguous. If you go for the sparge in a bucket method (which is what I do), there's no need to drain the grain in the bag after the initial lift as much of the remaining sugars will be caught by the sparge water anyway. I just briefly lift the bag up by (a gloved) hand in the stockpot/urn, carefully gather one corner from the bottom, then twist for a minute or so and most of it will drain out back into the pot/urn. In the mean time (or before lifting the bag if you're clever), put a kettle- full of near- boiling water into a second bucket/pot, then drop the bag into it and pour over another kettle- full of hot water and as BribieG says, stir the crap out of it. I leave the sparge for about 15 minutes, stirring a couple of times and then lift the bag again, twist and squeeze to recover the sparge water. Its after this sparge that you'll need to suspend it for longer to get as much of it back as you can, but twist before hanging it to condense it into a more solid mass which should drain the sparge more efficiently. Give it a squeeze and more twists from time to time while your boil proceeds and just keep adding this extra few cups of sweet stuff.
My kettle volume is around 2L, if smaller you just need more of them or use another pot on the stove and get it ready as the end of the mash approaches. My stove is out of action while the mash is on as the insulation will catch fire if I try to use it, so I sometimes use a camping stove to get the sparge water ready. This should be no problem for you though as you're using an urn.
The sparge in a bucket method allows the boil to get cracking while you attend to the sparging, generally by the time to skim some froth off the boil comes around, I'm just finishing the sparging. Interestingly, adding some cooler sparge to the boil will precipitate some more scummy froth and break, because I use a domestic gas stove my pot takes over half an hour to get up to boiling, so I am generally adding sparge water before boiling temperature is hit, so I can usually skim even more muck off it. Obviously once the boil is officially underway, skimming is probably going to be removing hops too, particularly if plugs or whole hops are used, so should be avoided.
Let us know if there's any dramas or other queries!