Ok im sorry but totally disagree with you guys. First off if your impeller is rubbing on the wear ring you have bigger issues. Correctly set up there is .25 wear ring to impeller clearance. I dont know why people make such a big deal about this. If your run your jet for more the 10 mins on the trailer i would run a second hose down the clean out and thats it. The packings are the only thing that can be hurt because they can make the shaft hot and burn the packings. The only other on to watch out for is if you have water lubed bowl bushings. If you berk still runs oil in the bowl (or grease) than run it.
Matt
Be careful.....The Berkeley type pumps rely on pump thrust to keep the shaft symmetrical to the pump housing, running the pump without this thrust (angular contact double row ball bearing) can cause impeller interference with the wear ring.
Been doing this since the early 80's and have owned more jets than I care to admit to....

Totally depends how the pump is built, I use an RV holding tank clean out wand tie wrapped to the loader (can't get my hand hole cover off). But with a stainless impeller and snug wear ring and snug fitting stuffer, I really don't do it.....Often...

It makes a lot of noise and sounds, well, expensive.

Number one thing to do is to spray the intake out with a high pressure water hose to clear any debris that could be in the pump, this could potentially clear small rocks/dirt from the wear ring area and saving you some grief. The intake of the pump is like a street sweeper while going down dirty/rocky roads....I used to use a place mat (like for a kid at the dinner table) duct taped to the intake on long road trips on the race boat, you should see the faces when I pull a 16"X20" picture of Elmo off the bottom of the boat....

GT