I do not know what is a mivac, but a rotavapor is one equipment where you use vaccum to reduce the boiling temperature of a misture and concentrate the extract. The boiling temperature depends on the absolute pressure (the vaccum ) employed. As an estimate adjust the pressure to the vapour pressure of the petroleum ether that is ok for your extract. The solvent will boil, leaving the ballon and will be condensed, flowin to the collector flask. Heat bath is used to provide energy of evaporation. As the first time I suggest you to use pure petroleum ether to adjust operational condition.

Rota-evaporator would be the ideal instrument for you. Now your extract will have the solvent and your product. If your solvent is a stable solid (non-volatile), then you can simply remove your solvent at a temperature, slightly higher than that of its boiling point.  At the end you may apply a little bit of vacuum. 

If your product is a volatile matter, then your problem becomes a bit complicated. In this case the boiling points of the solvent and the product have to be taken into consideration for the conditions to be followed during the separation process.

Petroleum ether is a mixed hydrocarbon solvent. Various grades of it with different boiling ranges are available in the market. If your compound is a volatile one, depending upon the product's boiling point, you may use n-pentane / n-hexane as solvent .