Some notes on the process for making a partigyle. I did a couple of things wrong and a few things right on Batch 100, so I thought I'd write down what should have happened for future reference.
Create a recipe of some sort, then use instructions at http://www.brewingtechniques.com/library/backissues/issue2.2/mosher.html and the chart at http://www.brewingtechniques.com/library/backissues/issue2.2/moshertable.html to figure out what the two parts will be.
Use both the HLT and BK to heat water. Heat just enough in the BK for mash in. Use whatever is appropriate for the recipe, but usually 1.25 - 1.5 quarts per pound of grain. This will leave your BK empty and ready to receive the first runnings.
Calculate 0.125 GALLONS per pound for grain absorption. Use hot water from the HLT to get enough for the first running. Example:
28.25 lbs grain
1.5 qts/lb x 28.25 = ~42 qts = 10.5 gallons
Heat 10.5 gallons of water in the BK to mash in temp. Use all of this water to mash in.
28.25 x 0.125 g/lb = 3.5 gallons lost to grain absorption
10.5 - 3.5 = volume of first running = 7 gallons. That should be about right for a 5 gallon batch with a 90 minute boil. If it is more than you need, make the mash a little thicker by adding less water for mash in, maybe use 1.25 qts/lb instead of 1.5 qts/lb. If it's not enough, add water from the HLT at the end of the mash to get exactly what you need.
Heat water for small beer in HLT at the same time water is heating in BK for mash in. This means hot water is available right away for using my heat exchanger to keep the mash temp constant. (This is a good procedure anyway, partigyle or not. It saves a little time and I don't need to worry about having hot water ready in time for the heat exchanger. The only downside is I need 2 propane tanks or I need to make a manifold.) Heat a couple of gallons extra in case you need it to top off the first runnings. Make sure there is at least enough for sparge for the small beer since the HLT is going to be the boil kettle for the small beer. Better is to heat a couple of gallons extra, just in case you need it. Do not calculate for absorption. Example:
Want 7 gallons in boil kettle for small beer. After first runnings are completely drained to the BK for the strong beer, add 7 gallons to the mash tun for the small beer.
Drain any remaining water in the HLT to a bucket. You might want it in case you come up short after collecting the wort for the small beer. If you get more wort than you wanted, collect it all and boil it down to the right volume. Otherwise, the beer will be smaller than you planned.
One mistake I made was I used whole hops and don't have a SS screen on my HLT, so the valve clogged right away when trying to drain into the fermenter. I used a scrubby on the end of my racking cane and siphoned. Next time, I'll either add a screen to the HLT or put the hops in nylons.