Clear Plastic Tube Help?

Hi guys. I want to know 2 things. Could I buy a clear plastic tube at a hardware store? Dumb question but I just want to know. I’m going to make a few BAD ASS bongs here soon. and #2 is what could i use to plug the bottom of the plastic tube. Oh and one more… how do i measure grommets? I hope you understand. Like how do I determine the size of a grommet that i will be inserting a marker tube into. Like how do I measure the marker to determine the size of the grommet that I will need. God I’m so high right now. But please do help me out. :rastabong