I flew with the foam clunk only and had issues. After asking around, a couple of others had fixed the problem with a header-tank - but I assume this does not apply for all engines/setups.. Try the foam clunk only first and see..!
I use the smallest tank I could find as a header tank (Heli-headers cost approx.4x the price...).

The way I plumbed it was as follows:
- Standard set up with clunk in the header-tank as well (some will argue here, but works for me)
- Vent of the main tank is standard (with check-valve)
- Hose from the clunk in the main tank goes into the "vent" of the header-tank
- Hose from the clunk in the header-tank goes to the engine.
- Fill the tank by using the hose from the clunk side of the header-tank..