Leaking drain taps

We are into the first week of a ten week trip through Qld. I noted at our first stop that 3 of our 4 tanks were dripping from the drainage taps.

We drained our tanks and had left these taps open for about 6 weeks after our last trip.

I have rotated these taps back & forth & experimented with different shutoff positions.

I have made a temporary fix with short pieces of hose from the outlet and wedged up in the chassis.

Has any experienced similar problems? And if so how did you fix it.(It would be simple for me to replace the taps if I were home.)

Neil