Re: silver solder?
as long as you cleaned everythign really good, and used flux with the solder, it'll be fine.
I put 2 fuel outlets in a tank with silver solder (not petcocks, copper tubing).
I also used silver solder to seal up holes, seams and gaps in a tank that I made.
Pressure test it with compressed air and water to check for leaks after you're done.