Most GATK tools apply several read filters by default. You can look up exactly what are the defaults for each tool in their respective Technical Documentation pages.
But sometimes you want to specify additional filters yourself (and before you ask, no, you cannot disable the default read filters used by a given tool). This is how you do it:
The --read-filter argument (or -rf for short) allows you to apply whatever read filters you'd like. For example, to add the MaxReadLengthFilter filter above to PrintReads, you just add this to your command line:
--read_filter MaxReadLength
Notice that when you specify a read filter, you need to strip the Filter part of its name off!
The read filter will be applied with its default value (which you can also look up in the Tech Docs for that filter). Now, if you want to specify a different value from the default, you pass the relevant argument by adding this right after the read filter:
--read_filter MaxReadLength -maxReadLength 76
It's important that you pass the argument right after the filter itself, otherwise the command line parser won't know that they're supposed to go together.
And of course, you can add as many filters as you like by using multiple copies of the --read_filter parameter:
--read_filter MaxReadLength --maxReadLength 76 --read_filter ZeroMappingQualityRead