I wonder if there is an actual problem such as uneven development that OP is trying to solve?
I use metal tanks also and takes probably 15 seconds or so to fill and empty. I've never seen any problem in the end result. I keep my development time greater than 5 minutes as that's what Kodak datasheet says. I find, if I tip the tank a little and aim at certain point in the opening, AND regulate the speed of pour, I can get good flow rate. I try not do it too fast where it starts to "burp."
If this question is a result of reading somewhere, uneven development could result from slow pour in/out and OP is not seeing an actual problem, then I'd not worry about it so much.