Help. Dishwasher won't drain.

My dishwasher won’t completely drain. There is a puddle in the bottom of the washer after it runs. I made sure there is no clog in the drain under the sink. The basket is clean and I also removed all gunk but it still won’t completely drain. I also noticed that the drain hose that runs under the sink runs in a sort of an S fashion from the washer to the drain because it is too long. It seems to me it should kind of run like an upside down U instead but I am no plumber to say the least. Could this be the problem? Also. what would make it only partially drain? Seems to me it should either drain completely or not at all but again I am far from knowing anything at all regarding plumbing or dishwashers.

Just noticed there is water remaining in the drain hose under the sink. Does this mean the drain hose is clogged and is the problem ?

Thanks in advance for any help.

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Help. Dishwasher won't drain.