The black goopy strings in the photo is probably the butyl tape. When you need to to install the rear floor service hole cover, you need to use some kind of butyl tape. Make sure to use it, that's what Toyota wants you to use to seal that area.
I did google butyl tape and this is what I did find. "Butyl is a common term used for the isobutylene isoprene elastomer. As the name implies, butyl is comprised of isobutylene with a small amount of isoprene. It is known for its excellent resistance to water, steam, alkalis, and oxygenated solvents. Another outstanding characteristic is low gas permeation. Butyl is capable of providing high energy absorption (dampening) and good hot tear strength. Good resistances to heat, abrasion, oxygen, ozone"