Question on trap countermeasures?

I checked the DMG and can't find anything about this.

When a trap or hazard is revealed to the party, what is the proper way to reveal possible countermeasures? Read them (without DCs of course)? Let people try things blindly? Or give them a rough idea of things they might be able to try?

I describe the trap, or at least whatever part of it the party detects, and let them come up with ideas. So when the party into a portcullis trap and detected the pressure plate I told them "you notice what appears to be a pressure plate in the floor here" and then they looked around and saw the lever that would raise the portcullis. They didn't know what exactly it triggered, but that gave them a couple of options. Some traps will be more obvious than others. Once they ask about what they might try I'll let them know if that approach seems like it might work and what skill to check against. I like that approach, it makes traps a bit like a puzzle to solve.

I don't know what "The One True Way" (tm) is, but I generally let the players try whatever they want and if what they describe falls under one of the countermeasure skills/things then I adjudicate it accordingly, else they 'don't see much effect from trying that' ... basically, treating it -kind of in a way- like a skill challenge.

but then again, i tend to prefer fairly rules-transparent encounters, so I don't often read out vulnerabilities/resistances against monsters and such... unless it's a really common one in which case they think 'this type of thing' might help , but i'd never spell it out exactly as to the game mechanics of the DC or amount needed/done.

Your group's style may differ from my own, so, of course, YMMV.

Very good question, and I've seen all sorts of different DM styles on this. Some rattle off everything there is to know about the trap for faster resolution. Some give a general description, and let you figure it out with trial/error. Some will hold off on the different bits until interacted with. It all really depends on the trap mechanics, complexity, and DM/Group style. There is nothing spelled out on how to run a trap, so it's all DM discretion.

I try to give descriptions and let them try things from there. For instance they step on a trigger plate, and four nozzles in the room start spewing fire. At this point I would tell them the fire produced seemed to be generated by some ignited fuel stored behind the nozzle, and there is a bellow that helps spray the fuel. At this point someone will tell me they want to make a dungeoneering check to see if it would be possible to exhaust the fuel, while someone else probably wants to make a perception check to see if there is a way to shut it off, and meanwhile the paladin is wanting to see what happens if he shoves his flamedrinker shield in front of a nozzle to let the rest of the party walk by safely. The paladin probably discovers his resistance is not enough to soak up all the flames, while the perceiver sees there are more nozzles that haven't yet been fired, which probably trigger off more plates in the room, and the dungeoneer figures out there might be a central fuel source, and knocking off one of the nozzles and dumping some fire down there might create a chain explosion to deplete all the fuel, and the cleric with an insight check tells him that might not be wise.

I just try to keep things going, if they seem stuck at any point, I'll start giving more descriptions. They might see a pattern in the arrangement of the nozzles which indicates a certain timing. A few perception checks later they might discover a similar pattern in the depressions of various pressure plates on the ground, and after an insight check, the acrobat may be on his way jumping and ducking through the gauntlet to get to the far end, when the last pressure plate turns the whole thing off, at the same time opening the rear wall up to reveal a half dozen blazing skeletons and a pair of hell hounds.

So, what I'm hearing, then, is there is no 'right' way. I'm kinda surprised that the DMG or DMG2 don't address this.

I decided to include a couple of traps in the last session - one was a hazard of a collapsing wall in a mine, and the other a spider web trap in a cave with a bunch of spiders. I realized in both cases after I described the situation, that there wasn't a easily apparent way to get around/out of the traps. So, I gave a rough idea of what could be attempted.

That just ended up feeling like a 'roll the dice, please' interaction. I will say, that in both cases, at least one group member came up with a unique way to approach the situation. In one case, the wizard just hovered over the area that triggered the wall collapse, and in the other, the ranger just touched his torch to the spiderweb, setting it alight (at which point, I started giving 2d10 damage to the web each round) until it burned up.

So, if it seems that everyone has a different way of approaching it, perhaps I could get a few people in the community to do a quick exercise for me.

Below is a trap I'm thinking of using in a traps only encounter. I'm curious how would other DMs reveal/describe the trap and reveal/describe the countermeasures?

Pond Muck Tentacle (noted as B on the grid)
Hazard
Level 11 Obstacle
XP 600

Four green and brown tentacles flail out from the water, dripping with muck from the pond, to attack everything within reach.

Hazard: These tentacles belong to a creature that that lives deep in the mud and detritus beneath the surface of a body of water, lashing out at all targets in reach.

Detection & Identification:
Perception: No check is required to see the tentacles.
Nature: DC 23 - These tentacle creatures are instinctive creatures that react to movement and pull any creature it can into the water and holds it underwater until it drowns. They then feed off of the decomposing flesh in the water.

Initiative: +6

Trigger: When a target gets within 2 squares of the water, the tentacles roll initiative. Each muck tentacle attacks individually until destroyed.

Attack: Standard Action Close burst 10
Target: All enemies or objects within reach
Attack: Close burst 10; +12 vs. Reflex
Hit: Target is pulled 4 squares. If the target is on land at the end of the pull, they are released. If they are pulled into the water, they are grabbed and held underwater (reveal the second countermeasure?) - Each round a character is underwater, they must make an Endurance 20 check. If they fail, they lose a healing surge. If out of healing surges, they lose hit points equal to their level.

Countermeasures:

• A character can attack a muck tentacle that has just attacked him or her, or that has just attacked a target adjacent to him or her. Each tentacle has AC 21, Fortitude 17, Reflex 20, and 60 hp. When 2 tentacles are destroyed, the remaining tentacles drop any grabbed creatures or objects and disappear beneath the water.
• A character underwater can attack a particularly vulnerable area of the tentacle where it springs from the pond mud (AC 18, Fortitude 16, Reflex 18). If they hit, it is severed and dies immediately. The mud does grant concealment (-2 to attack rolls).

That should work OK. I'd guess that PCs with ranged attacks will try to just stand back and pepper the tentacles though. Of course that won't work too well if they stay submerged as long as there's nothing in range.

Like you suggested, I'd base most the descriptions off the triggers. Encounter may go something like this:

DM: You see tentacles flailing around in the pond.
Ranger: I shoot one.
DM: Your arrow is swatted away by a tentacle, and the tentacles withdraw briefly. Doesn't look like you can destroy these tentacles while they are in the water. Maybe if you lure them out.
Fighter: How far away can the tentacles reach?
DM: Hard to tell, but nature boy over there might be able to.
Ranger: Nature check, 30!
DM: (reads monster info, and reveals reach)
Fighter: Ok, I will move to where I think the edge of their reach is and ready an action to grab one of the tentacles when it attacks me, you shoot it then.
DM: One of the tentacles shoots out of the water as you approach make an initiative check, if you beat it's initiative you can ready your action to grab the tentacle.
(initiatives are rolled)
Ranger: I go first, I ready an action to shoot a tentacle if it gets far enough out of the water.
Fighter: I'm next, my action is readied.
(Tentacle shoots out, ranger puts a few arrows into it, fighter grabs the tentacle, tentacle grabs fighter back, and pulls him into the water).
Fighter: Oops, didn't think it would be that strong.
DM: While you're under water, it's murky but make me a perception check.
Fighter: Ok, ugh, I got a 12.
DM: It's too murky you see nothing.
Ranger: Darn, now I'm going to have to go save him, I put away my bow and rush to the edge of the water.
Fighter: I make an athletics check to get out of it's grasp, 17.
DM: That's dead on, you escape it's grasp, and avoid taking drowning damage and losing surges.
Fighter: Whew, didn't know about that. Then I move out of the water.
DM: This time two tentacles shoot out, and you are both grabbed and in the water.
Ranger: Arrgh, should have stayed away.
DM: Well now that you're in the water, make a Perception check.
Ranger: 28.
DM: That's great. You put together what you know from your nature check and what you see in the water to find a weak spot at the root of the tentacles in the water.
Ranger: Great what do I need to do?
DM: Stabbing it in the weak spot might work.
Ranger: Ugh, with my 10 strength, yeah not likely, can I throw a dagger?
DM: That won't be very effective under water.
Ranger: Yeah, didn't think so. Okay, here goes nothing I pull out my non-magical dagger, wait, two daggers, minor, minor, one in each hand, and try to twin strike it, that at least gives me two shots. Can it be quarried?
DM: No, you think if you can just connect it will collapse.
Ranger: Great, didn't have the extra action to do it anyways, twin strike it is, and I'll use elven accuracy if I have to.
(after some rolling the ranger takes it down)
DM: Good job, now based on your earlier nature check, if you can take down one more, you think the other tentacles should retreat and leave you alone.

So now they know all the dangers and countermeasures. I added a perception check on the fly to see the vulnerable spot. I think it's warranted in the murky water.

If the countermeasures are obvious, I describe them because I'm counting on them to try them.

If the countermeasures are not obvious, I ask for an appropiate check to reveal it.
In this case I may announce that one of the things you can do is to spend a [Standard, Move or Minor] action to perform the check and get additional info about the trap.

So, bottom line, I wan't players to know all the options they have.

There's no point to design or have an option that nevers gets used.
Too much wasted effort.