Xaul nods and says 'This isn't gonna go well for me I don't think.' He then follows behind Damros, ignoring the quiet crackle of burning floorboards coming from nearby.

Skye is barely beyond the first rung of the ladder, bringing up the rear, before the half-orc’s cry is heard and he comes leaping down from above. 

“What was up there? Zhent? Guards?”

Xaul just says 'Ummm....there was a tavern'

Damros will slow and walk beside Skye, filling her in on the chaos Xaul left in his wake after the abrupt crashing entry into the tavern.

Sehaethas groans when he hears what happened above. Begins to wonder if he's gotten involved with then entire party of crazy warlocks like Kylaski.

After a further 5 minutes of walking, the pathway opens up into a junction (map will be sent once I get on my laptop in the morning). On the opposite side to you is a raised platform with a door, and there is a couple of arrow slots in the walls in either side. 

Skye steps back, into the nearest cover, before whispering what she has seen. 

 Map above (Blue circle is approx party location. For scale, the circle is about 5ft (one square on map), and north is up.) The triangle to the north west and south east of the roundabout are the arrow slits.

[How high up is the raised platform with the door? Could the party climb up to reach it?]

(Could Arson solve this problem? Asking for a friend). 

You are currently in 1ft deep sewage. The ledge is about 2ft tall (so 1ft above the sewer). It is easy to get up

Xaul looks around at the crossroads and says 'I'd like to get up and investigate that door there, though I suspect that when we pass by the arrow slits, we'll be ambushed.' He scratches his chin to think of a solution, then says 'I suggest that we take our tinderboxes and set the flammable sewer gas alight to-' [Nah just kidding, what he really says is:] 'I suggest that we either sneak or run past, or investigate the arrow slits closer from a safe distance before we continue to avoid taking any damage.' From where he's standing, Xaul will look at the arrow slit across from him and will try and see if he spots anything stationed behind it. Perception/Investigation (the modifier is equal): 3

You see no sign of anything currently on the other side, from where you are right now 

Skye takes her waterskin and stifles a sigh. She pours the water into the sewer, then dips the waterskin under the surface until it is full. From there it is a relatively simple and unpleasant matter to aim the waterskin opening towards one of the arrow slits and then use her armpit to squeeze it violently, sending a jet of sewage into the arrow slit in a long, yellow fountain of-- well. 

It's probably the same way it got into the sewer as its getting out of it, she thinks. 

Roll a basic dex check. And then roll me a second d20. Let's see if things become more interesting 

Dex: 5

D20: 5, also  

Xaul justs stands and watches, mouth agape as Skye tries to squirt the waste into the arrow slit. He then says ‘I can replenish our water supplies anytime, so let’s give this a go.’ He then does the same as Skye, emptying his water skin and filling it with sludge, before violently spraying it against the walls of the sewers, no apparent aim or direction, just caking everything in waste. 

Dex: Nat 1 for a total of 3 
Raw D20 roll: 13

Neither of you manage to get any sludge to actually go through the arrow slit. Some lands on the wall of the slit but then pours back out. Xaul's waterskin seems especially caked in the sludge. It will take a good deal of cleaning before that is safe to drink.

Xaul groans. 'Well that was a waste of time, I dunno what I was actually trying to achieve there but looks like I've ruined this waterskin for now.' He then says to the party. 'I'm going to go up that ledge and check the door. If there were cultists stationed in the arrow slits I think they would have shown themselves or moved after all our horsing about.' He then goes from where he's standing to the ledge, climbs up, and checks to see if the door is locked.

It is not locked