it is the hopblocker, and I've measured the amount, albeit with hops, trub et al at around .75gal (from a 12 gal batch).
narvin - I'm still going back and forth on whether to use the hopblocker or not. on the one hand, if I use it, I get 90-95% clean wort into the fermenter and need to only dump a little bit, if any at all, from the cone. but am short on my target volume a bit.
on the other, if I runoff with no screen, i do suck up a good deal of goop that comes out with a dump of 1-2 quarts.
I'm still debating which works best for me - I've been doing so for months now, however.