you will need to put in about 3.3 grams in the bottom part secure everything with hot glue:

(print with supports touching build plate)

you may find that the tube is a little to long preventing it from closing, if that use some sand paper to make it shorter, once you put the weights in you can "combine the two shells" put some hot glue near the end of the tube and on the base where the shells make contact  so water can't come in. when mounting the float on the line ad a rubber float stopper to adjust the height of the float like this: