SHORT ANSWER: 1/2 day to several days depending on the product

LONG ANSWER: This answer depends greatly on the type of material being used.  With some acrylic products we've been able to stretch 1 tube out for several days (proper flushing at the end of day and lubrication the following day).  Even with some silicone and urethane we have been able to get several days out of a tube depending on the atmospheric conditions.  I have also had tubes not perform well after coming back from lunch just because of the conditions on the roof.  You might try thinking of these as a paint roller.  In many cases, it will cost more to try and clean a roof tube than to simply grab a new one.   

Short answer: Depends on materials... In most cases YES...

Long answer: The Roof Tube can be cleaned and re-used succesfully, but only up to a certain point before the inner part of the tube and packings start to deteriorate. Think of them like paint rollers. Obvoiusly for Acrylics you can flush with water although you may need to relubricate the tube. For silicone's and poly urethanes you can flush with mineral spirits or xylene depending on your materials.

SHORT ANSWER: Buy them all 

LONG ANSWER: No really you should buy them all... Or at least a couple of our bundle packs.  Each type of mastic draws and expels very different.  We recommend trying many different tip set ups to find the PERFECT combination.  If you are trying the Roof Tube for the first time with a new product, allow the first 1/2 hour for experimenting to find the best combination.  If you are unable to draw a product, move to a bigger tip. If the product is dispensing too fast and becoming costly and messy, move to a smaller tip or try adjusting the ball valve to slow the flow.