Drain pump assembly for a washing machine appliance and methods of operating the same

A washing machine appliance comprising:

• a sump for collecting wash fluid;
• a drain pump assembly in fluid communication with the sump for selectively draining the wash fluid collected within the sump;
• a water level detection system fluidly coupled to the sump for measuring a sump pressure;
• and
• a controller operably coupled to the water level detection system and the drain pump assembly, the controller being configured for:
• setting an empty sump flag after operating the drain pump assembly to empty the sump of the wash fluid;
• determining that the sump pressure is greater than a predetermined pressure threshold after setting the empty sump flag;
• setting a pre-cycle drain flag in response to determining that the sump pressure is greater than the predetermined pressure threshold after setting the empty sump flag;
• and
• operating the drain pump assembly to perform a drain cycle and empty the sump of the wash fluid at the beginning of a subsequent operating cycle only if the pre-cycle drain flag is set.