Crews from Tumble and Llandeilo were called to a farm in Maesybont, Llanarthne, at 20:40 GMT on Thursday.
A "Coldcut Cobra" ultra-high pressure water jet, which is on trial with Mid and West Wales Fire and Rescue Service, was used to tackle the blaze.
An environmental protection unit was also sent to reduce the risk of pollution.
A large timber and tyre fire which burned throughout the night in Carmarthenshire has been extinguished.