I've never tried Soylent, but I do have the UK equivalent - Huel [1]. This isn't as simple as drinking it, because you need to measure it out, add water and mix it for a minute or two. Then when it comes to cleaning, it isn't just a cup. There is also this grid like piece of plastic that helps to break up chunks of Huel but is hard to clean.
I like the idea; but in reality I'd rather jut have some toast if I want something quick. I know it's not as good for me but food is more than just getting calories and nutrients in. I get pleasure from eating a variety of textures and flavours.
So you're using that plastic cup that comes with the first order? I always thought that cup's just a gimmick that people use when trying it out for the first few times [1], and if they like it, they would start preparing it with a blender.
[1] I still have to try it out. I can't quite get myself to order the smallest pack (a full week's supply) when I don't even know if I like it.