The sexual act of placing a finger in your female sexual partners anal canal and vaginal canal simultaneosly to check her viscosity of either entrance. Then as the mechanic on duty you determine if she is a quart low and you give it her anally or vaginally after you attain the proper lubrication on your dipstick.
Lastnight as a part of foreplay I gave Jane a "two finger mexican oil change prior to having sex"
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