Please don't feel badly just because I brought this up. I see you defending your actions, and I didn't mean to generate that line of thinking. Cleaning skimmers is a pet peeve of mine. I was visiting Servo's new 400g system yesterday, and his skimmer had the same foul buildup in the riser tube and I talked with him about it. Since I was there, he felt obligated to show me how easy it was to clean it, but he didn't actually clean the riser tube, only what he could reach within the cup with some paper towels.
If you are cleaning it every 3 days, that should be good enough. The reason I clean my daily is as I stated above, and that is why I built my sump the way I did. I wanted easy access to that so I wouldn't be lacsidasical about that necessary duty.
H20eng makes square skimmers, but usually the only place that needs cleaning is the collection cup area. Even with his design, a magnet wouldn't do the job.