Another thought came to me

For the plastic tube of the proper size , you may also want to look at the many household cleaners that have a squirter mechanism on the bottle ... take them apart and they all have some sort of dip tube inside... I just looked at a Windex one and it might even work...looked a little fat .. check them all out..
WD-40 has an aiming tube that come on the side of the can are also small , but they are short and might be a little too small
Keep looking around.. you may have something right in the house..