Water leak?

Its probably leaking and will continue to leak. Its doesnt matter if its under pressure or not. However, that doesnt tell you why the water is not draining. Its a good chance something solid is in there and needs to be snaked out. If your not familiar with the work, I would call a plumber.

p.s. Usually after the sink makes the turn in the wall it meets up with the vent pipe ( you would see a pipe sticking out of the roof above the sink area). Sometimes an animal will fall down the vent or drop stuff in. That sometimes causes the clogs.

Call the plumber and don't waste time. The joint is leaking and some thing has the pipe badly stopped. If running the drain cleaners through and the hot water (boiling would dissolve grease and at least move it) didn't help you have a more serious problem. If it is showing through the bricks then it is a more serious problem because of the possible damage to flooring and inside walls due to water damage to the structure. If it is the one sink doing it then don't use it and see what they (the plumber) can do but either way minimize or stop using that drain until the leak is fixed. The problem could actually be in the main line out rather then that one joint; you can check that by not using that drain but running a load of clothes through and seeing if you have any leakage-if that is true then the main line or a major line is clogged and they will need to run a drain snake through it but you still still get the joint repaired. The pressure of the plunger should not cause the joint to leak and once it starts it won't stop completely; if it is minor it might not leak any more because water won't back up to it but anytime the water backs up it will so you could continue to damage the frame of your house until it is actually fixed.

You don't say if the heater is electric or gas. If it is gas replace it. If you have a electric heater check two things first. Check to see if one of the elements are bad. When a element burns out water will start to leak around the bad element. Also check to see if the drain valve will drain, if not replace the heater.If you buy a new heater remove the drain valve that comes with the new heater and install a ball valve with a water hose connector. You will have a 3/4 in. hole to help flush out the sediment that will build up in the bottom. If you drain 5 gallons of water every two months your new heater will last a life time. Good luck.

First of all, I commend you for even going for the trap. Much farther than I would have done. =)

Plumbing is one of those things where, even though you know you might have write a check you don't want to write, it's best to call the professional. Especially if you see water leaking outside of the house, it's probably bigger than just that particular drain you were trying to clean. I would call someone right away, too, because if it's leaking you might be in for a huge water bill, and that would make writing the check a whole lot worse.

Yes you need to have your pipes cleaned with a snake.

Call a good drain cleaning company.

Better call that plumber.

PLUMBER HERE I WONT CHARGE YOU DOLLARS I LIVE IN LONDON UK LOL

UNDO THE NUTS AND REPLACE THE RUBBER OLIVES

Don't you just hate it when things like that happen. I always see dollar signs!