Maintain your black water tank by adding water softener through the toilet every third fill. The softener will keep solid matter from sticking to the inside of the tank and the drain plumbing.
This may help even when stuck.
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Mark & Susan
Lehighton, Pennsylvania
EAGLE HT FIFTH WHEEL | 30.5CKTS - '13 Ford F150 SCREW - PullRite Superslide - Roadmaster Active Suspension Member - "Northeast Adventures RV Rally Group" & "Mason-Dixon Bunch"