[chevyjaxon]

I have an overflow box too. the U tube can be gently lifted up and down to shake the air bubble out. open your wallet and buy an aqualifter, I leave mine running constantly, it ensures that incase of a power outage, I will get a siphon when the power comes back on. also try to get a fitting on your return line that you can have the tip of it sticking above the water, this will prevent any "hum sucking". rubber hoses although great at noise reduction arent as reliable as pvc and threaded fittings but again thats all a matter of personal preference. a really great reliable, powerful and inexpensive pump is a rio HP series the only con is its noisy. try 2 smaller heaters instead. good luck.