I have used the 2 liter bottle cut up but the tin foild works better to me and the bag works... I am gonna spray clean it anyway with brake cleaner so it's a whole lot quicker with the bag.

 

It has never been necessary to put thread tape or dope on drain plugs that have an o-ring. Doing so only pushes the o-ring out of it's intended groove thereby promoting leaks. And thread tape only promotes galling of the delicate aluminum threads in the cases.
I was in the hydraulic business for 30+ years and never saw an SAE threaded drain plug w/o-ring that required dope or tape to seal the threads.
Pipe dope and tape is for pipe threads only.

 

All my bike's drain plugs were dopped from the factory, but I think they just do that as a precaution so they don't leak on the showroom floor... looks bad! I've never used it, I just inspect the o-rings and replace them when they start getting chewed up. No leaks yet.

 

Agreed.