Clay For Mr Farthing

Mr Wantage and Fred finish their work in Trumpton and go off to the Chigley pottery to mend Harry Farthing's phone. There, they find that the trouble is due to clay in the receiver holder. Harry gives them a demonstration of how he makes a bowl. The PO engineers mention that a lot of clay was dug out when the new telephone exchange was built, and they give Harry a lift to the exchange in their van. They tell Harry he can have it all, but how can they transport it back to the pottery ?