Rinsing various foods is a great idea; frozen seafoods (silversides, shrimp) especially can be loaded with phosphates. I tend to think it's a big deal to rinse it only with tank water or RO/DI water, why risk adding anything? A turkey baster and fine mesh strainer works great- little bits of finely minced/chopped food, rinsed through the strainer with the baster, and the water thrown out and the food hand-fed with the baster to anemones, fish etc.
The more finely chopped/minced, the easier to digest.