if money is no object, buy another tank, but otherwise, 4 on tap isn't so bad. I have a 7cf with a collar and can fit 3 cornys and a 5 gallon sanke (which is slightly bigger) with room to spare, but not enough for 5. I don't own 5 cornys to test if I would have enough room for them without the sanke 1/6th barrel. My collar isn't wide enough for the 5th keg on the hump. My tank is 20# so, it doesn't even fit on the hump, so I drilled through the collar.