Create another TO of Oil Sample Data
I assume a field in Oil Sample Data for Equipment
Create a global field in Oil Samples (gEquipment)
Link the new TO to Oil Samples by:
SamplingSet = OilSampleData::Sampl Set AND
OilSample::gEquipment = OilSeampleData::Equipment
Put the portal on your layout based on Oil Samples, and also the gEquipment field. Base the portal on the new TO and use fields from the new TO.
Now when you change the field "OilSamples::gEquipment", the related records will change and the portal will populate with the ones you want.
Thanks Ninja! Works perfectly :D