JollyRodger has it, I think. I always use a sight glass pre and post filter. Seems that on some tanks, the yeast sticks a bit to the cone. When the beer level gets to the cone, the yeast dislodges and slides down to plug things up. Don't know how to solve this with P&F. I keep my DE filter pressure quite low during the run with loose perlite. When yeast chunks dislodge and come to the filter, I use all remaining body feed and slow down the beer flow rate to allow pressure to build slowly. Always manage to get the batch filtered in a reasonable time and with reasonable perlite doses. Except with Oatmeal Stout. Beta glucans bind up even loose perlite in that. Good luck!
Phillip Kelm--Palau Brewing Company Manager--