RE: RCGF Engines
I would use the Hayes medium neoprene line inside your tank. It fits over the clunk inlet very well. If you use the yellow tygon, you can heat it with a heat gun and slide it over the inlet. I prefer the neoprene. You can also make a barb by buying a brass tube one size larger than the brass tube in your tank, and then cutting it into 1/8" sections with a dremel tool. I then sand off the rough edges and solder the section over the fuel tubing. Works great. If you go the Hayes neoprene route, I suggest cutting a section of brass tube, chamfering the ends so they are smooth, and inserting it into the fuel line between the clunk and the brass tube that goes through the stopper. Make it about two inches long, and center it between the clunk and the stopper. This will prevent the clunk from going all the way forward in the tank. Safety wire is spiffy, but a small zip tie will do as well.
Hope that helps,
Sam