I have a brand new whirlpool dishwasher that doesn't drain completely after running a full cycle but it will drain completely if I press the cancel/drain button.

I run the waste hose directly into the sink disposal with no air gap. I took the hose out and pressed the cancel/drain button and it had a pretty steady flow into a bucket. There also didn't seem to be any blockage at the hose/disposal interface.

I've read that water draining is a timed thing so a limited flow can cause a partial drain. I don't think that the flow was limited when it was going into the bucket, so I'm thinking could there be some pressure/blockage problem in the disposal? The sink drains fine. Any other suggestions, things to try?