I have seen some use them to help reduce bubbles. Also saw one that was pretty neat, guy used a 4" section of pvc, he cut large teeth out of the bottom and simply had his drain tube go into the 4" pvc, trapped all his bubbles without adding a baffle.
OP: if water level is fluctuating alot that would point me to think that the water is siphoning itself, then releasing. As stated, make sure your durso is 1/4" larger diameter than your bulkhead (use a reducer at the bulk head)