I've always seen that goop in connection with parasite cleanses and shedding of biofilms. Folk who carry out hardcore (1-3 month) cleanses can see material of that sort, that is enough to have lined the entire inside of the gut from small intestine to anus.
I've seen this material one time after using Bentonite clay, it was attached to the bentonite. I have associated it in my mind with the biofilms that candida forms (because it has a fungal form, it uses sugars to create cross-linked firbes, and thus a sugary 'nest' for itself), though biofilms usually contain lots of different species of bacteria, viruses, fungi and sometimes parasite eggs.
If you felt unwell before it came out, and you're on a parasite cleanse, keep going! Biofilms can make you feel utterly awful when they are dying/detatched.
Uhmm.. where can you see more biofilm gook?
The dark side of YouTube and the parasites forum. Sometimes they're brownish because the food came out with 'em.