Basslines are easier than drums because you can just filter out the highs and the upper half of the mids and you got a somewhat doable bass to work with.
Drums, I use a noise gate. Play around with the threshold, attack and decay until you hear ONLY the drums come through the gate, of course you'll have artifacts from other sounds but drums usually hit hard and very quickly covering up almost everything in their small footprint. Chop them up from there.
To add to LampDog's post keep in mind that the shorter the portion that you sample the larger the wave form will be with more detail to make it easier for you to zero in on the drum hits.
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