8822 has a lot of dust. If that dust isn't reasonably removed, It can create a paste that will clog screens and seal plumbing.
If your cleaning procedure changed from loading one system to the other, you might be seeing reduced flow characteristics from more silt.
It is tempting to load containers and rinse in place with hoses. Unless that garden hose flow rate is good, it may allow the caking effect to happen somewhere later on.
If you like the convenience of loading and rinsing in the bucket, only loading and washing in layers (3-4") at a time might help.
Better results might come from first wetting down the 8822 in bulk, and then transfer it to the container with a strainer (or whatever), and then rinse with a hose in the container. You'll see a bunch of shitty contaminated water drip through the strainer as you pull it out. It seems like this process really reduces the overall quantity of dust before it comes near a component of the system. As a result, your final flush in the bucket is more likely to carry the crap through, rather than accumulate the cakey paste in the bottom of your bucket/tailpiece screen.
8822 is much more porous (less compact-able) than coco, and roots are much less likely to stall in the tail piece (for lack of crowded soggy shittyness). If you combine roots filling the drainage gaps with an extra bit of unrised silty dust, you've got your shitstank right there.
My guess is that you've got too much high speed shit going on at once for any user error.
I'd suggest upping your rinsing regime on the 8822, and/or consider changing your tail piece to a larger diameter. I ran my earliest PPKs with 3" PVC and unseals. It is relatively easy--and was documented somewhere (I forget who)--to make a small slice off a matching coupling and glue it in place to get the ring overlap that you're accustomed to from the 'tailpiece'. Recall that there is much more volume in one 3" tailpiece than 3x1"... and more volume should require more shit to clog it.
Ashes plumbed the system with 1/2 feeds teed out of 1" main lines for pulse, and nothing on the supply/drainage side was ever smaller than 3/4.
Shit will always accumulate in plumbing over time. So flush regularly, and/or oversize on new builds.
Dave--this is a media issue, not a PPK mechanic. All systems that flow will fail when something stops that flow. It's not the PPK. It's the clog. Recall that the primary media in this system was turface, than coco, for a long time. Recall that D9 already had extensive experience and procedures associated with running turface, and coco needs to be rinsed to get the shitty salts that come with it out. 8822 as a media alternative is relatively new on the 'scene', and the kinks need to get worked out. Rinse, Rinse, Rinse... and maybe now be aware of root clogging.
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Im finally starting to reach my goals. 
