The problem that Christ presented them with - was one where they were infringing ever so slightly on one of the Ten Commandments with the "CORBAN" rule - but later in Mark 7 he points out that "pot washing problem".
Then the Pharisees and some of the scribes came together to Him, having come from Jerusalem. 2 Now when they saw some of His disciples eat bread with defiled, that is, with unwashed hands, they found fault. 3 For the Pharisees and all the Jews do not eat unless they wash their hands in a special way, holding the tradition of the elders. 4 When they come from the marketplace, they do not eat unless they wash. And there are many other things which they have received and hold, like the washing of cups, pitchers, copper vessels, and couches.
5 Then the Pharisees and scribes asked Him, “Why do Your disciples not walk according to the tradition of the elders, but eat bread with unwashed hands?”...
14 When He had called all the multitude to Himself, He said to them, “Hear Me, everyone, and understand: 15 There is nothing that enters a man from outside which can defile him; but the things which come out of him, those are the things that defile a man. 16 If anyone has ears to hear, let him hear!”
17 When He had entered a house away from the crowd, His disciples asked Him concerning the parable. 18 So He said to them, “Are you thus without understanding also? Do you not perceive that whatever enters a man from outside cannot defile him, 19 because it does not enter his heart but his stomach, and is eliminated, thus purifying all foods?” 20 And He said, “What comes out of a man, that defiles a man. 21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, 22 thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. 23 All these evil things come from within and defile a man.”
The subject was "sin" -- "Evil" - the washing was ceremonial - "baptismo" - they were dipping in water to remove sin that may have been encountered in the market place. Same with the pots.
Of course we know that poison, bacteria etc can get on your hands or on the pots and kill you or bring sickness ... but that was not the issue. Christ was addressing the man-made tradition/fiction that "sin" was a substance you could get from the market place (for example) coming in contact with gentiles - and so you needed to baptize the utensils, your fingers - cleanse them from sin or else sin would get in you - from what you ate ... and you would be guilty of the sins Jesus lists. He says that is all mere "fluff" -- mere man made commands being taught 'as doctrine'.