If you run your drain line (fuel dot) to the bottom of the tank, it will do it's job. It does not need the complexity of a clunk added, to properly drain the tank.

It is imperative to have the vent line, or entire tank for that matter, sealed. No leaks.

Most R/Cers do not know about this type of venting, but it is superior to the standard method. It is standard in CL stunt flying.

Anybody ever fly a CL plane? The engines go lean at the end of the tank, if a standard vent is used. Any successful CL model is either using a Uniflow tank, or a pressure system.