So, went against trying to keep the old tank, bulge in the back of tank that shouldnt be there, big hole in the top that shouldnt be there and a failed liner internally, added up to I just dont want to deal with it

.
Before I have a new tank made or buy the 760usd tank, I managed to find another tank, albeit its sat in a field for 10yrs, i gave it a quick wash out and have identified 7 small holes., the good thing is they are all at the top of the tank.
Currently just running a watr based de rusting solution inside it, then when its back in the ute will throw some gravel into the tank and hopefully clean it up better internally.
So brazing is the path I am going to go with fixing the 7 small holes.
When brazing, should i just try and smooth fill like lead wiping or shou.d I cut a small piece of steel up and braze it in, does it have to be steel?, can I use brass etc
Trying to be on the safe side, even though its sat empty for so long, is it safer to braze it when its 3/4 filled internally with water or is it best just having it empty.