With various types of plumbing systems whether solar heating systems, hydronic heating systems or just regular home plumbing it is common for gate type drain valves to leak (see picture 1).

The valve will often leak when it gets old or if something gets caught on the seal. Most people will just leave a small drip and not worry about it. If you have a machined cap for the drain you can install that and be done. Although getting a metal cap can sometimes be difficult and they are never right at hand. An easy solution if you have access to a plastic bottle of soda is to take the cap from the soda bottle (I know pepsi works) and screw that onto the drain. Voila a quick and easy solution to that leaking boiler drain, hose bibb, washing machine connection or drain on your solar heating system. (see picture 2)