The procedure for flushing a vacuum pump is relatively simple.  First place a small amount of HyVac flushing oil in one of the clear glass containers.  This is to compare against flushing oil drained from pump after the procedure.

Run the pump till the sump is warm roughly half and hour. Make sure the pump is  disconnected from the electrical source.  Open drain port at base of pump using a wrench or your hand.  Drain the pump of the used vacuum pump oil while the pump is warm.   Tilt the pump so as much of the used oil is drained from the pump and if possible rotate the pump mechanism manually.  This usually applies to belt drive pumps.  Especially with piston style belt drive pumps like HyVac 1 or PressoVac pumps because their oil sump design holds oil in the pump until the pulley is rotated a few times.  Repeat this step.

Place funnel in exhaust port of the vacuum pump and fill pump to halfway up the sight glass with HyVac Flushing Oil.  Turn pump on and adjust oil level more if needed.

Run pump for about half an hour and alternately activate the gas ballast valve on the top of the pump.  This helps agitate the oil in the pump.

Disconnect pump from electrical source and drain the flushing oil as per the procedure outlined above.

Place a sample of the drained oil in the second container and compare color and sediment levels with the original virgin sample.  The sample drained should be close to the color of the original sample.  If the oil is very discolored then a second flushing should be considered.

After a good color on the flushing oil is achieved the pump should be drained of all flushing oil and filled with new vacuum pump oil.  Clean you work area and the pump with a rag to remove any spilled oil.

If possible the samples of the flushing oil can be discarded and a fresh sample of the pump oil can be placed in one of the glass containers and sealed for future reference against the quality of the new oil put in the pump to monitor it's quality in service.