At the risk of sounding idiotic, I will ask this question anyway...
Next class, we will be doing the rainbow transfer cake. There are 4 different icing colors in the rainbow. If I am using disposable bags for each color, what do I do about the tip? Do I need to buy extra tips? I wouldn't think I could use the same tip for each color.
How did the rest of you do this?
Get a couple couplers, they will save your life. trust me. you just put one end in your bag, cut the bag to fit, put the tip on and attach the other end of it. when you change colors just undo it and remove the tip wash it and put it on the other bag. hope this made sense. HTH
I can see washing it here at home, but what about during class? I didn't see a sink in the room where we are. So, that got me thinking that I would need to have four of the same tip in order to do the rainbow. Maybe I am just too tired and not thinking clearly.
I think I had a couple of tips, but if you take your tip off of one color and put it on the next, just squeeze the extra frosting out and you should be able to use it on the next color. Maybe try to plan it so you start with your lightest color and work to the darkest? I don't know I see what you are saying though. If you are planning on decorating cakes very often you may just want to invest in some extra star tips, you will use them all of the time for shells. Good Luck! 
We were NOT allowed to wash any of our tips, and stuff in the sink at Micheals... Because of all grease clogging the drains...So we had extra tips and couplers . That is a good point as well.
I guess I will just go and buy some more star tips and be done with it.
Still, I am curious to know how others who took the Wilton course handled this situation.
I used the same tip, for the rainbow cake while in class. I just moved the tip to the next bag and squeezed out the last color into it's bowl until the new color started coming through. There will only be a little color in the tip, so it will not take to much time to push it out! 
Luckily I was able to wash my tips as there was a sink there and we were allowed.
What about buying a small packages of baby type wipes and using those and paper towels? Just an idea. I tend to use baby wipes for a lot of things when there's no access to a sink (but then again I currently have a toddler). My husband uses them for even more things than I do. They do come in handy.
scrapmomof3- I would invest in a few more tips. I have tons of them and I use alot when I am doing different designs. I see you are from Orlando, I live in Ocoee.... Some Florida cc family members are going to get together I think next month (oh and an Alabama member) want me to email you when we do? 
Faye
Do you "have" to do the raiinbow cake? Just curious, I'm a WMI and I never have my students do the rainbow transfer. I let them decorate their cakes however they want with the option of doing that transfer or bringing a coloring book page (with not many details) from home or choosing an entirely different design. But in answer to your question about the tips, definitely would buy more couplers and tips, it will save you SO much time, it's worth the extra few dollars!!!
Buy extra #16 tips. You will always have uses for them. Sometimes I have 4 colours going at the same time and need the same tips. Maybe its just me but I have several ones, twos threes etc. It is only the really obscure tips that I only have one of.
Or you can push through the colour as others have suggested. That works too and it will add to the colour mix of a rainbow if you get a little of the colour that is beside it in the next colour. Like floating a colour when painting.
Good luck. Claire
Ginger....yes, we have to do the rainbow cake. I think the book gave the option of a character pan or rainbow...the instructor said the character would take too long to do in class.
Faye....I used to live near Ocoee, off of Hiawassee (until that turned into what it is now). Now, I am in the Longwood area.
Please let me know when you have your get-together. With 3 kids, I can't promise I can attend, but will see what I can do.
Lisa
scrapmomof3,
I made sure I had extra tips to do the rainbow. I now have extra of a lot of the tips that I use frequently. It definitely saves time. It is so much easier to just be able to pick up a bag of icing and use it than have to change the tip and then start using it.
Bradymom
Florida get together is March 24th at 10 AM-1PM. Pot lunch. See link for Jacksonville.
I've had students do many different things.
Have couplers on each of the color bag and switch the tip out. You can wipe it out as much as you can or just put it on the other bag and squeeze a bit of the icing out before you start the next thing.
Or you can buy additional tips, to save the cleaning the tip step.
I personally feel you can not have too many couplers or multiplies of tips you use alot. 
My instructor is pretty much going by the book. She is very informative.
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