RE: 2 Klunk/Pump Setup
Fuel line from carb into tank goes to the clunk.
Pressure line from the muffler goes to the clunk and is attached to it's side about 1/2" short.
Vent line goes to top of tank and is only uncapped when fueling tank.
Fairly simple and easy to make. And it's the simplest uniflow setup.
There are variations that create a better setup for fueling, like with a t-line connection with check valve or such. The way the above is worked for fueling is that you pull the "stopper" on the vent line, then pull the pressure line off the muffler and fuel into there. When the vent line spits fuel, the tank if full. Put the stopper back in the vent line, plug the pressure line back on the muffler and crank that puppy up. Needless to say, you have to have access to the pressure line and the vent line for this to be an easy-to-use setup. And also needless to say, you can make it easier to use with some t-connections etc.
Uniflow works great. Having the muffler pressure blowing very near the fuel pickup in the tank sounds bad, but trust me, they've been working great for years and years and years.
Only special detail you need to keep in mind is that both the pickup line and pressure line will be attached to the clunk so the clunk is going to have to move two hoses with gravity. So make the interior hoses SOFT ones.
But truth is, in most RC aircraft, you really don't need uniflow. but if you have a plane that won't work well with the normal setup, the uniflow is easy to try for a fix and will very often help.