Teh bulkhead is what makes the seal at the tank. there should be a gasket on the inside of the tank inside of the bulkhead.
If this is leaking you should be able to turn the large plastic nut on the bulkhead to tighten it down. Normally you would tighten it to hand tight plus a quarter turn more witha wrench.
Sometimes there is a piece of dirt or something else stuck in that gasket that allows water to leak out of it.
But try turning that nut bit more.
It may be that you ahve to remove the water to below that level then remove that gasket and check it and or replace it.
If the pipe is already glued to the bulkhead, that would mean that you would have to cut teh pipe, replace the bulkhead replace teh pipe, reglue and all that good stuff.
If this was done for you at the store, they should fix it. I am not sure what kind of warranty they would have to make them come out and do it at your house and such, but give them a call.
If it is the seal that is leaking, it will look like water is running down the back side of the glass, (running / dripping) directly from that bulkhead. the threads on the bulkhead will be dry, the only thing wet will be the glass and the stand under the tank under the bulkhead.
I ahve heard some peopleuse silicone for small leaks, but I would not suggest that as a fix, unless you drain the tank dry out the problem area and then silicone it.
As for the bubbles, yes the overflow makes bubbles, The standpipe, (durso) or otehr design is to minimize the amount of bubbles / distance taht the water falls. These devices, (pipe assemblies) usually have some form of adjustment, (slide them up and down) to adjust the bubbles / noise
Also when the water goes into the sump / filter, there is a water falling noise, that can also be adjusted by placing the drain pipe up or down above or even below the water, again to minimize the distance the water falls. You can add a piece of pipe to lower the pipe into the water. I use a filter sock to help dispurse the wter as it hits the sump and also strain the bubbles.
You can look at some of my pics, (I am missing a bunch as my daughter takes teh camera from me for football games and I dont see it until she brings it back
Ideally you dont want any noise or bubbles, so adjust and tinker until you are happy.
Good luck.
