I believe the 2003 is the same layout as ours. If so, the check valve Kelvin is talking about is under the bathroom sink counter in the back right corner. I removed ours also, but the flush still would not work. I have tried filling the black tank all the way up and letting it stay that way for 3 months with Ridex in it trying to dissolve any hardened particles, but still will not work. If yours ends up that way, I can show you how to install a permanent wand flusher that you can bring out from under the trap door in the bathroom to use and connect to a fitting that is in the outside refrigerator door.