Originally Posted by Aces11
Here's a pic of my pump with a T-valve. I have 2 outlets with only one stone so I did the opposite of you but it works the same way.
Set up that way actually decreases the air flow compared to running both lines separately. You don't actually need an airstone on the end of the hose unless the bubbling noise is too loud/bothers you. Try running just one line directly and see how much difference there is compared running both lines into the tee. I tried the same thing with a larger air pump (Whisper AP 300) and then ran the lines separately to get more flow.
I usually do split each line into 2 tanks with a tee though, and use the single inline air valves to regulate/balance the air flow.