I just installed a new ge dishwasher and when I hooked up the drain hose to the dishwasher I noticed a rubber piece blocking the hole, instead of reading the manual I just cut it off. Well turns out the was suppose to stay on. Did I mess up the dishwasher and have to get a new part or can I run it with out the rubber check valve?
That is a backflow preventer to keep the drain water from returning to the tub. If you're draining to a disposal or some point higher than the hose connection you'll get dirty drain water back in the sump without this piece. You probably should replace it.