Originally Posted by Dr Dave
You won't get the choice when you remove the filter.
A small drop out of the sump plug would be best imo.
I would let a cup full out via the loose sump plug, then another clean cup full for sampling, that way you'll be into the main sump oil, not just getting bits from the sump plug thread! Wipe the sump plug first too.
That's how we take power transformer oil samples at work, we always use two containers, one to flush through the sample petcock, and a second one to catch the clean sample for analysis.
You can always put he excess back in the top!