The phrase take it with a grain of salt is an English idiom meaning, "Be skeptical about it." The "it" is usually a statement heard from someone else, like a factual claim or advice. It can also mean that while the statement is true, it might include some error or it might not be true when applied in every circumstance; you will need to take care and use common sense when applying it.
The image of a mountain of salt is humor, exaggerating the usual "grain". It suggests that the advice is almost certainly wrong, maybe even deliberately wrong.
Historically, the expression with a grain of salt comes from reports by the ancient Romans, such as Pliny the Elder in the Naturalis Historia, that adding a grain of salt to a certain recipe or to poisons could make you immune to poisons; see here for a little more information. Most English speakers today don't hear any reference to poisons when they hear the idiom, but the grain of salt vaguely suggests protection from something mildly dangerous in the thing that you are taking it with.