[Radek]

It wasn't - but in my experience you can always pass. Here are some tricks that work sometimes:
1. If you have Witch's Stick or a similar sleep casting weapon, put the filth in a sleep and push the sleeping filth before you. You can emerge from the water enough for taking a breath sometimes.
2. Select the smallest character as a "leader".
Otherwise, try, try, try, ... If you cannot get out then return underwater into the tunnel and try again (trying to get out while you are stuck in the orifice of the tunnel is usually futile). If you lose your nerves then you can give up without any consequences. The only thing you need is to get the correct answers for the Naga spirit somehow. Here are the correct answers:

serpent strikes - servant prays
serpent charms - servant bows
serpent schemes - servant dreams
serpent sleeps - servant waits

The first part is a hint given by the spirit, the second part is (the minimum of) the correct answer you have to type in. For example, if you get a hint "serpent strikes" then type in "servant prays" (without the quotation marks) and so on.