[Delphinus]

The first thing I would suggest is stop feeding via the sump and letting the return pump be the distributor of food. I feed using a mini-turkey baster and shooting the food towards the intended recipients, plus, I'll take a wad of food and bury it into the sand (for the nass and the worms and the 'pods). I don't like the food to go through any pumps, if it does, then I have to clean out my pumps more often ("more work" == "less good"). Even though some food might go over the overflow into your sump, it's not going to go back into your return pump in anywhere near the numbers high enough to cause a big problem there.

Unless you're getting an ammonia/nitrite spike from the food caught in the return piping (unlikely), I wouldn't go to heroic lengths to clean out the pipes. They get pretty gross anyways over time. So long as there's no restriction in flow, they're OK. What you could do is close off all but two of the returns so that you have the most flow through one output, blast out any lingering crud that might be there; and then repeat for the other two outputs.

Unfortunately I have to get back to work, I'm not really allowed to surf anymore during the day. :( But maybe I can think about this and be able post some more ideas when I get home.