Bottles are plastic and have a wide opening for easy filling. The suggested method for using them: when adding a Guard Dog product to plain oil, according to “How to Use,” pour the specified amount of plain oil into the appropriate bottle. Pour out the plain oil into an empty bottle of oil. Replace that oil taken out with the specified amount of the Guard Dog product.

Retain the plain oil in the bottle, and continue to use that bottle for future treatments. After few changes, enough plain oil will have been retained to eliminate the purchase of one bottle of plain oil for a subsequent oil change.