1) San Marino, Harmony, Harmony Plus, Niagara, Sure Spa, Twin, Rhine, Atlantic, Neva Plus, Tiny: the drain plug is on the left corner of bottom (same side of control panel)

 

2) Other models: the drain plug is on the right corner of bottom (same side of control panel) 

 

Destiny

3) Destiny is on the opposite side to control panel as in above picture