A picture would help some but I believe you are talking about the exhaust relief ports...most outboards will have one or two on the midsection of the engine...there will be water kind of spitting out of this at idle on most when they are warmed up and "in water" some won't do it on muffs...the pee hole as described earlier should have a nice steady stream of water coming out of it....weather on muffs or in the water. It just tells you that your water pump is working...it normally exits out at an angle so you can see it...some will exit straight out the back but most at an angle so you can see them when your in the boat. The main exhaust exits out under the water as said before so they are not loud on the water. I really think you are talking about the exhaust relief ports though...if you put your hand over it or them if there are two you will feel some exhaust coming out...not a whole lot but some...they are there to releive some of the pressure....you'll see smoke coming out of them from time to time also...ecspecially on a cold start up.
Sounds to me like you have carbon build up in the engine. We have to remember that our two stroke out boards are some of the hardest working engines out there...how many gears do you go through to get to your top end?? none...it has to go from a standstill to full speed with one gear. Thats why propping is so important on outboards...if you are overpropped by even a little to put you at the lower end or below the recommended rpm range you are lugging the engine...not only at low rpm but also at wot. Think of it as an old car or truck that gets lugged around by someone...every now and again it was always good to go out and blow the soot out of an older engine...that soot was carbon build up. On a two stroke our oil is either mixed by hand or by mechanical means...VRO..etc...When we ease around alot, overmix our oil a little bit, or our oil injection sends a little more oil than we need that oil that doesn't get burnt either comes out as smoke or it builds up...eventually coming out as sludge as you described. This sluge can be a bad thing as it gets on the rings and causes a situation we call coking....thats carbon build up on the rings...if this carbon gets hard the rings eventually will "stick" and even break off. Then poof goes the engine.
All this being said, thats why your BRP xd100 and I believe x50 and your Merc Premium plus have additives in them such as "ring free" or "seafoam" those are not whats in there as each manufacturer will put their own additives in there oil...this help keep coking from happening. If you are running a regular two stroke oil...xd25 xd30 merc premium or penzzoil or any of these they do not have an additive in them to prevent coking. This is where products like seafoam, ringfree, and others you'll see at walmart or your marine store ie...bass pro, gander mountain, etc... come in. If your outboard is dripping sludge you need to do a "decarb" and soon. There are COUNTLESS ways to do this...I use seafoam...I actually run 3/4 can in 12gal about every 3rd tank in my old ranger. Then once a year I take a 3gal gas cantainer, put one gallon of gas in it, put 3/4 can of seafoam in it...if you premix your oil put the recommended amount probably 50:1 in it...if you have oil injection you'll have to see how its hooked up first...if anything you can just run the fuel line from the fuel tank and hook it to your 3gal container. Put the remainder in a spray bottle....go to the lake and run for about 10 five or ten minutes...stop and fish or just sit around for 15 mins...start up and do that again...repeat this until you run out of gas....hook your gas tank back up...pull cowling off and spray the rest of the seafoam in the carbs while the engine is running...when you are done with that put cowling back on and let her rip. You can also do this in your driveway on muffs, just do not rev it up...never rev an outboard on muffs as they can run away without any pressure on them. If you go to the lake or something to do it take a spare set of plugs with you...you'll need to replace them when your done. After you do this run seafoam or an additive like it every few tanks and you will not have any carbon buildup or sludge anymore. Just to let you know when you do this, you'll see ALOT of black stuff from the exhaust and exhaust relief ports...this is the carbon build up coming out. If its real bad you can also spray seafoam in each cylinder and let it set over night. Hope this was clearer than mud and sorry for it being so long...pm me if you have a question or anything. Most shops can do a decarb also. I just really think if you have sludge coming out of it you need to decarb soon...as there is no telling how much buildup there is. If you go to iboats.com and look up decarb you will see more information about it. There was a post a while back about seafoam and I posted some links to a GREAT write up about decarbing and the hows and whys of it if you can find it.
"But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord.” Joshua 25:15