I've changed oil on my cars for as long as I can remember. I changed the oil on the Boss 302 yesterday afternoon.

I've always just drained the pan, then replaced the bolt and moved onto changing the filter.

This time around I drained the pan, hand tightened the bolt and then changed the filter. I then went back to the pan bolt, removed it, and another cup or so of oil came out.

I guess there may be some type of vacuum in the system, and it gets relieved when you remove the filter?

Anyways, just thought I'd share to see if anyone else has had the same experience.

I'll be following the new steps from here on out to make sure I get as much of the used oil out as I can.