Sorry for the slow reply [mention]Pinchons[/mention] . I'm usually better than this. I'm stuck on a small computer so I can't give as much detail as I usually would. Even scrolling takes forever!
Now, I know I did write recently about the "Sweet Liquor Shops."
If you search my posts for that phrase, you'll get some links to the answer you are looking for. It's afew posts above so study that.
But, let's also look at it a different way.
Before we get to tea...
Sparging is
not a normal practice in SVAG brewing (Single-Vessel All-Grain - e.g. pure BIAB). It
is normal practice in MVAG brewing (Multi-Vessel All-Grain Brewing such as batch or fly-sparging methods). If your kettle is too small to do SVAG brewing, you are forced to compromise on something - labour, ingredients and/or time. This is dealt with in the Sweet Liquor Shop posts.
Let's think on tea
Let's say you are making a cup of tea with a tea bag. Do you fill half-fill one mug with hot water, soak your tea bag in that, then take the tea bag out and add it to a second mug half-full of hot water, then dump the tea bag and then pour the contents from one mug to the other to make a full cup of tea?
No, you don't. That would be stupid.
What about if you wanted really strong tea? Say, four tea bags to a cup?
You can put all four tea bags into one mug and fill it with hot water. When you pull the tea bags out, the mug will not be quite full. You now have two choices: top the mug up with a little water or add some water to a second mug, dump the four tea bags in that and then drain the tea from that back into the first mug. You'll get a little bit more value from your tea bags but it has cost you time, labour and some calculations.
Brewing is a bit like tea bags
An average brew is a bit like using say three tea bags. You would never notice the volume loss is a mug using one tea bag but with three you might see a bit as those tea bags absorb liquid that you never see again.
If you were using five tea bags (a strong brew with say an Original Gravity of 1.080) maybe, maybe, maybe???, you might think about using a second mug (vessel) to get a bit more out of those tea bags and fill the space left in the first mug after you pulled them.
Over-Extraction
I'm not going to address that here however, there is yet another layer to all this. All I'll say here is that we'll move on to coffee. Coffee, like your barley, wheat etc, only has so much "goodness" in it. Go to a coffee shop and imagine you have just ordered an espresso/flat white/cappucino but the barista simply left the (can't remember the name of the damn thing) "filter with the handle thing" in the machine and pressed the water button. You would be getting the second runnings of the coffee which has no goodness left. In fact, it is much worse as not only has all the goodness gone into the customer's cup before you, only bad stuff remains and there is plenty of it.
I could write more but I think I'm done for today on this one
PP
If you have found
the above or anything else of value on BIABrewer.info, consider supporting us by
getting some BIPs!
. And, when you find the bit you were looking for, then you have to remember where you put your beer before you went looking for the gadget. It's a very vicious circle 
.
I have not done that before so could not say. If this is what you have to do so there is beer remaining after the boil - give it a shot! 
Does anyone have advice?
