I think i may of figured it out..i believe the part is called a "Check Valve "... i will see if i can replace it without having to remove the whole pvc tee with sensor
You can hear the water flow back into the pump. Back check valve. Little Giant 89695 CV-10 Condensate Pump Check Valve for VCC, VCM, VCMA and VCL-14/24, 1/4-inch MNPT x 3/8-inch Barbed, Black https://www.amazon.com/dp/B000WR50VA/ref=cm_sw_r_apan_glt_fabc_66WYKXCQAA8PQA7JB492?_encoding=UTF8&psc=1
Normally there'd be a "check valve", perhaps it is stuck?