A negative note. When I got my tank back from the platers the inside had a thin layer of rust that wasn't there before. I imagine they didn't rinse and dry the inside very well. Eventually I decided to use POR15 to line the tank. No problems with that (yet). I suggest you make a point of asking them to protect the interior of the tank.
The shop I went to asked if i could make plugs to fill the tank holes for them, they want the tanks to sink in the chemical bath. I dont know what they use to fill them up with, but they cannot be hollow or they float on top of course.
When I was done they kept the plugs I made for future use. Being America, we dont see too much BSSP thread.
I had a little flash rust on the underside near the central mount hole. I used some baking soda and water, then a rust converter on it. I wish they would have rinsed better too, but even rinse water is expensive in plating. Here, every ounce of it has to be captured and carted off as waste. I figure it must get used over and over (the rinse water) until someone notices its not doing that great a job anymore.
Lee