The mould used is one designed to achieve a flow canal within the product. Flash due to welding both halfs of the mould together will interfere with the flow pattern of the liquid; We have to deal with a certain level of flash on the inside of the flow canal.

Q: how can we deal with this flash so the velocity of the flow passing through the canal is at its slowest?

or

Q: how can we position the flash so it sits in this section of the flow, where the velocity is least?