2007 3400RL Kitchen Gray Water Leak

[English Lake Montana]

Hi. Well after discovering a lot of water laying above the axles in the belly of my 2007 Montana 3400RL I removed the black plastic section on the bottom and cut and peeled back the foil insulation. I then started filling the gray water tank in the kitchen. I also removed the two plastic access hole covers that are on the base cabinet so I could see where the drain pipe goes into the tank from the top. So I am laying underneath on my creeper waiting to spot any leakage. When the tank was full, water started leaking pretty heavy around the corner of the tank where the drain pipe from the kitchen sink goes in. So I know the leak is either a crack in the black plastic tank right by the drain pipe hole or a loose or cracked drain pipe. Is it common for a leak to occur there when the gray tank is comletely full? An RV repair shop told me that the pipe connection to the tank is either glued or has a rubber grommet that the drain pipe passes through. If it is a rubber grommet than that would explain the leak when the tank is completely full.
What is the easiest way to get access to those drain pipes? I thought of removing the counter top or cutting a larger access hole in the inside side of the base cabinet and buying a cabinet door to cover the larger hole. I just have to make sure that a door mounted in that area where there are no doors or drawers would not obstruct any drawers near the sink that I would have to open. The unit is 100 miles north of where I live so I won't know for sure until this weekend. They sure could make it easier for you to get to the plumbing in cases like this.
I just purchased this RV used a month ago and was never told of a second gray tank so the only gray tank I was dumping was the one for the shower and vanity. That is the reason the tank was allowed to get that full in the first place. Thanks to MOC members for pointing the second tank out to me.
Thanks