Cleaning up a Valk with totally gunked up carbs & I need some experienced info on what's what inside. Please excuse my ignorance here, I'm a decent wrench but carb work is my weak suit!

Looking at the pic I am assuming the big jet in the middle is the "main jet" and the smaller one to it's right is the "slow jet". Both of them are slotted and removable. I also assume that they would need to be squeaky clean & the passages under them clean & open.
Am I right so far??
If so, what is the little brass tube to the left of the biggest jet? It does not appear to be removable & I cannot get a wire through it.
I want to get this Valk running great again & learn about Valk carbs along the way.
Thanks!