How to intersect objects and delete leftover internal planes? I'm trying to find a simple way to create vertices where two objects intersect and delete the leftover internal planes + then join the meshes so that I have one hollow mesh to sculpt.
The reason I need to know this is that on my first sculpt I just joined the meshes, but it didn't create vertices at the intersecting points so when I went to sculpt it just overlapped the meshes as you can see here in the neck.

Here is what I am working on now, it needs to be 1 hollow mesh
Select the objects and hit Ctrl+J to join them into one object, change to edit mode and select the meshes you want to intersect, hit Ctrl+F and select Intersect (Knife) from the menu and change to Self Intersect in operator panel.



After the operation is done, intersecting edges will be selected and you can mark them as seams Ctrl+E>Mark Seam, then select internal faces using L button when hovering with the mouse cursor over internal faces while in face selection mode.