What is it that plugs it up? Is it the same material (twigs, grass, rocks...other) all the time? One item that can plug up the pee passage is the water pump impeller when it starts to disintegrate. It isn't that is it? If you don't know what is causing the plugging then you probably aren't cleaning it right.
If you are simply using wire or trimmer string to push up into the nozzle and try a clear the tube, you are just pushing the debris back up out of the way temporarily and it will come back down the passage and clog the tip again.
You need to do two things:
First, check your water pump pickup screen at the bottom of the gear case and ensure that it is not broken or torn so that it is filtering debris as it should.
If that checks out, you then need to go under the hood and physically remove the rubber tube for the pee hole and try to identify what is in either the tube or the engine block where the tube attaches. If you find little hard pieces of rubber, then you need to service your water pump.
What I find a lot in the motors I work on is tiny little twigs or stems. The twigs like to get stuck in the engine just before entering the rubber tube and I have to dig to get them out. Another common thing is really small little pebbles that come down the tube and stick in the nozzle tip. It will all depend on where and how you use the motor. If you go into shallow water frequently, you can expect some clogging, especially if you are kicking up sand and mud.
Note how the rubber tube is routed before removing it. If you install it incorrectly, it will kink and always seem clogged. Hold the tube up to the light and make sure it is clear before reassembling. Same thing with the nozzle. If the rubber tube is stiff or kinked, replace it. They don't last forever.
Another thing I do before reassembly of the tube and nozzle is that I run the motor in a test tank and allow the water to gush out of the engine so that I know the block passage is absolutely clear. I can't think of anything else at the moment so try these things and good luck.