So I'm trying to rig one of these mixamo models up in Houdini, as they don't provide an auto-rigging tool for Houdini (It works brilliantly in Maya ), and I'm struggling with the painting of weights.

Since the model comes in as parts bits of the mesh are being left behind because I can't paint under geometry that naturally covers it. Boots for example underneath trousers.

How do you deal with this? ops:

without seeing your model I'd say use delete nodes to separate these overlapping bits, then paint the larger or bottom of the the two - then you can use attribute transfer to put the painted values onto the not yet painted one - then do touch ups on that one…

instead of delete
use Visibility SOP to temporarily hide occluding parts of geo, Visibility doesn't change your geo so you can bypass it afterwards and your weights that you painted downstream from that node will be still fine

you can as well hide geo by selecting polys you want to hide and pick Hide Selected Primitives form tool Visibility menu
it will place Visibility SOP for you

visibility will work but I find it can be troublesome to use if you have lots of bits…and having more isolated pieces of geometry will paint faster…
but everyone finds their own workflow.

Thank you for the advice guys I will take both into considerations. I actually only have three or four separate geometries so the visibility node might be the way to go.