You can start a siphon without sucking the air out of it as follows : Fill the siphon with water, put a finger over each end (1, Fig. 53), place one end in a tumbler full of water and remove the finger under water (2, Fig. 53), then remove the other finger. Does the siphon start?
In this case the water you pour into the siphon drives the air out, and this is the reason you do not need to suck the air out.
Fig. 53. Starting A Siphon
Fig. 54. Siphoning Sand
Arrange a siphon (Fig. 54), start the water flowing, and then pour sand or mud into the upper tumbler. Is the sand or mud siphoned over into the lower tumbler?
Attach a long tube to the outer arm of the siphon and repeat the experiment. Is the sand or mud siphoned more rapidly and more thoroughly ?