One thing to keep in mind when using new plastic is the mold release that may be left on the plastic. Notice some feels kind of slick at first? Since I don't know what this might be and since everything has some potential to have something like insecticide sprayed on in the storeroom, I do a bit of work to just clear any doubts.
A half cup of bleach and filled with water can be very cheap and easy insurance. Drain, rinse and then treat as if it were tap water and you can be sure any mold releases, etc. is safe. The difference between a bleach soak and tap water is the amount of water diluting the chlorine.
I wash my plate before I eat just because I want to know what is on the plate, so I do much the same for my fish where they have to live.