How do you filter your frying oil to make sure it doesn't contaminate your vegetarian products?

All of McDonald's U.K. restaurants filter vats in the same order and in sequence at least once a day. The vats are filtered in the following order: Fries and Veggie Goujons, Pies, Chicken, and Filet-o-Fish®. The unit is then cleaned before being used again. This procedure has been monitored and approved by the Vegetarian Society who have certified that our Fries and Red Pepper & Pesto Goujons are suitable for vegetarians.