An SCR injection system for an internal combustion engine is disclosed. Under certain conditions, reductant fluid supplied by the system may form deposits in a reductant injector. In order to dissolve the deposits, a reductant supply line includes at least a portion with a downward slope that is disposed above a reductant inlet of the reductant injector. This allows reductant fluid in the sloped portion to flow to the reductant inlet due to gravity. Advantageously, a bent portion is provided between the reductant inlet and the sloped portion in order to trap reductant fluid that may flow back towards the reductant injector when the system is purged.