drain is usually located at bottom where spray arm is, mine has a strainer cup that must be cleaned regularly.
The drain hose is underneath and usually requires pulling out the unit.
This happene dto me once and if I recall it was an eletric switch like a solenoid that wouldn't click over to the drain cycle.
What I always do is twice a year run a cycle with vinegar, helps keep the drain hose clear of grease.
Good luck | 
Maytag dishwasher won't drain 
