use a new tube everytime. doesnt seam like it would bother anything but it can.
you have to think. when you aireate you are pulling crap in it. then you push the fluid in BUT you'll never get it 100% out unless you sterilize it. then it just sits in the tube for 2-3 days and you could push it back into your body...NOT good idea.
You can get tubes with needles for like $3 for a pack of 10. Stick with that. screw sterilizeing tubes..not worth possibly getting an infection.
ouch!