Apply the filter to Pipes, Pipe Fittings etc. Pipe Systems are conceptual element that are applied to pipes, fixtures etc.

Yes that's exactly what I have. I check pipes, pipe fittings, pipe accessories, pipe placeholders, pipe systems but I set the contitional statements to System Classification Equals...I even tried Does Not Equal.

The criteria value could be the culprit. Try something simple like Contains and Sanitary or Cold etc. Simplify to see if your criteria is not worded or spelled exactly. Double check the System Classifications are showing up in the properties of the elements you're validating it against.

I used the 2018 sample MEP model, to link, to create the screen capture.

Thanks for your help Steve.

Having trouble with filters is so...2009. Hello??? It's 2018. I can't believe I'm stuck on this.

Yes I'm literally doing exactly what you're showing. I wondered if having my floor plan in the Coordination discipline was affecting me.

So I changed it to Mechanical. Nope.

I also wondered if another filter I had was interfering. It's a single filter with the conditional statements System Classification Does Not Equal Sanitary AND System Classification Does Not Equal Vent - unchecked in my view template so that only drainage systems show. This works perfectly for my own content...but not for linked content. Linked domestic and natural gas systems are still shown. I know this because I modeled a pair of domestic water pipes and a gas pipe and I get the ole "none of the created elements are visible" warning. I also toggled floor plan discipline to Coordination and also Mechanical.

This is the strangest thing to get tripped up over. I literally have a hundred different filters defined for various linked models and a variety of my own content. They all work except on the mechanical engineer's model.

I hope there's a solution to this so I look forward to any other input you may have. I'm hoping it's a really dumb mistake I'm making. Thanks again, cheers.

Can you share their model, privately if necessary? If so, email me a link to download it via steve at AEC Advantage dot com

Simplify the filter with just one criteria to prove your filter is finding the elements. Put your own pipe in the model to see if it works locally on your own stuff. Open up their model and look at their work, maybe they’ve done something unexpected, like use a CAD pipe software for the piping and you’re looking at a DWG.

If you are using a View Template, reference this thread, and try my solution in post #4 to see if this is possibly the issue:

If everything you want to filter is already in a workset you can also create a filter by workset, which is usually effective with linked models.
You may need to make a workset with the same name in your own model for it to work.

Otherwise whether the link is set to 'Underlay' or not can affect how it looks.

Is it possible that they are using a different system classification to model gas or waste water?
Gas piping is often modelled as 'Other'.
Many countries (ie. other than the US...) dont use Fixture Units for waste water calcs, so when using calculations based on flow rates it is necessary to model waste water with Hydronic Return.

Shudder.

And a dead-end workflow to establish if you ever receive standalone/discarded-workset models.

It's all entirely possible to do this OOTB - and my advice (on top of all else suggested) is you define your filters first with a "catch all" NOT condition (aim it first at something you know you don't want to collect) then an AND for the condition you are looking for.

As an example, our "Colour all MEP" and "Colour all Structure" and filters (which aren't actually called that) follow the concept:
find: all elements
where: <condition> NOT... (ours)
AND
where: <condition> IS... (the thing you are hunting for)

Tannar may be on to something, if the link is being overridden then the Filter needs to be applied at the override level, not at the top level outside the link.