another new tank

[AndyL]

Stinky, do yourself a favour, don't bother with a ball valve or "gate valve" (as sold at western pump - actually a knife valve) to throttle the overflow down, www.mcmastercarr.com sells proper gate valves (threaded adjuster). Otherwise you'll be fiddling forever trying to get it right.

Albert - stop taking credit, you didn't come up with this design. Search RC for silent overflow, it's well detailed there.