I purchased an aquarium testing kit, Pawfly. It does not use the usual oblong shaped bottles, but instead round bottles. The test tubes are also a bit thicker than others. I later glued two additional cylinders in the back for a large syringe and a pippet. I just used the test tube cylinder for the pippet. It might need to be a bit taller, but the pippet hasn't fallen out yet when moving the thing around so meh.

** If you're not sure this will fit your kit, I would chop away at this within your slicer, perhaps cutting away so it is just Nitrite. It is the lowest/already on the ground and would have BOTH the bottle and test tube sizes. You can even cut away the letters as well as make the base thinner.... just my 2 cents for testing. Anyway, hopefully this works for you!

Happy printing!