The wetness left over by rinsing mouth is overlooked because of it being unavoidable. Just make sure that you do not gargle deep such that some water from gargling goes down your throat. Just rinse you mouth and not gargle. The wetness of the miswak itself (sap) is overlooked as well. However wetting a miswak and using it is avoidable. Hence such water must not go down your throat. Since it endangers you passing water down the throat, it is makruh to wet miswak and use it.