So, what kind of strategies do you guys use to break back into the middle of Urchin Underpass when you're zoned out by snipers on both sides? I see this situation occasionally in randoms but I'm mostly thinking of my splatgaf games last night. Felt like my options were limited with the Dual Squelcher, but no one else on my team was having much luck either.
I feel like this is one of the tougher chokepoints to break through when you're losing, so it's going to be difficult no matter what your setup is. Especially depending on the skill of the two snipers in your example. If they are theoretically playing "perfectly," then obviously a lot of this discussion is moot. But for your example, I'll just assume good snipers who can pick you off regularly, but occasionally loses you if you're tricky.
Dual Squelcher, I've found there is very little you can do in this situation, other than continue to paint repeatedly over the hill, build special, and give your teammates an Echolocator. Just your presence, continually firing toward them, is good for keeping the enemy temporarily busy. Sometimes the Echolocator gives your teammates the chance to take out the ground soldiers, sometimes the opportunity is wasted. If you do start getting a decent push going, it's probably your job to try to get the near sniper if you can.
If you have Inkzooka, you can wait to build up special and then poke over the hill to surprise attack the sniper at your team's perch. You could go down the hallway and try to get him with the Inkzooka, depending on if he's doing hallway patrol or pressuring from the perch. The first Inkzooka shot is obviously the most important one, so make sure you aim extra carefully to get that guy.
Waiting for Bubbler or Kraken is a decent strategy. I've seen some rounds turned around by a miracle Kraken splat read that creates a lot of temporary chaos. You're going to have to get rid of one of the snipers in the chaos, and find cover from the other one, however.
.96 Gal, sometimes you can just fire mindlessly over the hill and pick off a couple ground soldiers who aren't being careful. Same with Seekers.
Splash Wall has a couple options, either approaching in the sniper hallway or standing on top of the little hill at the entrance and trying to create a zone. Sprinkler is okay for a temporary distraction, but not that great for this scenario in my experience. The other team is usually organized enough to get rid of it quickly.
I don't usually like the other entrance (the dropdown one) because you're so exposed and alone in the other team's ink, and the other sniper can see you come down. If you're Bubbler'ing, it could be a good approach if you want to pincer the people guarding the entrance, however.
Those are some of my experiences. They often don't work, but it can be turned around. I think the real key is just being patient, not rushing into a lot of dumb deaths over that hill, and waiting for you and your teammates' specials to build up. Sometimes the other team will get a little too greedy and end up getting splatted themselves, so they could create openings for you on their own. You're often just waiting for one random kill or special to get an attempt going.
EDIT: Wow, I wrote more than I expected to.