Mysterious Russian sovl

Neck too thick. You need a normal-sized bottle and to screw it in.

The goal is somewhat close to use of a bottle for urination during a traffic jam. Suppose you need a method of defecation that allows you to safely isolate the waste material in absence of more conservative options.

Just use a plastic bag like a normal bum.

It doesn't have to be water tight because (hopefully) your shit is solid enough to be contained.

then why use a bottle? Just get a bucket with a lid.

and line the bucket with a plastic bag for easy disposal. plus you can easily reuse the bucket this way

I only have bottle.