I forgot to mention...
The oil in your vacuum pump may already have DMS dissolved in it. If the smell persists even when you are not actively vacuum distilling DMSO, the vacuum pump could probably use an oil change. The bleach solution suggestion I made previously should cut down on the smell, and when you are finished distilling DMSO, I'd recommend an oil change. I don't think DMS (gas) dissolved in pump oil will significantly hurt your vacuum pump's effectiveness, but if you are actually getting DMSO (liquid, high boiling, unlikely) or other solvents (liquid, low boiling, likely) that are escaping the trap and ending up in your pump oil, your pump's performance will suffer. However, the same thing (high bp) that makes vacuum distillation of DMSO necessary make it unlikely that it would carry past your ice traps into the pump oil. Ethyl acetate, THF, dicloromethane, and other low-boiling organic solvents are much more likely to foul your pump oil than DMSO, as long as there is some sort of cold trap in use at all times. After completing the distillation, check the ice trap to see if there is solvent condensed in it. With a dry ice or liquid nitrogen trap, expect DMSO to remain in solid form until it warms up closer to room temperature. Be sure to pour off this trapped DMSO before turning the pump back on, or a small amount might be sucked into the pump oil if someone tries to use the pump without filling the ice trap (which happens ALL the time).