If you really used a "gas hose" for the water line then neither it, nor its fittings, are meant for contact with water, nor the pressure in a water line. I have no idea what a "stainless steel flexible hose" was, but it also may not be the proper device. Drain pans usually have so means of connecting a pipe to them, unless someone forgot to give it to you. If you do have a connection, rather than just a "hole", the run "something" to the drain pit. If teh relief valve were to open, it would flood and overflow the drain pan in a matter of seconds, so it SHOULD run to the drain pit, but NOT be connected to any "drainage" pipe. By "instant solder" I assume you mean tinning flux, and if so it is NOT a replacement for solder, but just a backup for poorly prepared joints.