This is similar to Matthew, chapter 26:18, and Luke, chapter 22:11. Mark indicated that Jesus told his 2 unnamed disciples what to say to the proprietor or the owner of the house, as he entered it (καὶ ὅπου ἐὰν εἰσέλθῃ εἴπατε τῷ οἰκοδεσπότῃ). They were to say that the teacher asked him where his guest room was (ὅτι Ὁ Διδάσκαλος λέγει Ποῦ ἐστιν τὸ κατάλυμά μου). Jesus wanted to eat the Passover at this house with his disciples (ὅπου τὸ πάσχα μετὰ τῶν μαθητῶν μου φάγω). This Passover was the remembrance of the Israelites fleeing Egypt by eating special foods. There is no indication of whose house this was or who the owner of the house was. Certainly, it was someone who knew Jesus.
Mark was extremely descriptive here just as Matthew, chapter 15:17, explained this problem about unclean food. Mark indicated that Jesus seemed a little upset that they still did not understand what he was telling them about defilement. Jesus said that any food did not enter the heart (ὅτι οὐκ εἰσπορεύεται αὐτοῦ εἰς τὴν καρδίαν), but the stomach or belly (ἀλλ’ εἰς τὴν κοιλίαν). From the stomach, it flowed out in a bowel movement that ended up in a sewer, latrine, or dung heap (καὶ εἰς τὸν ἀφεδρῶνα ἐκπορεύεται). There was a famous saying that it is harder to sell corn after it has been eaten by a pig than before it was eaten. Whatever went into your mouth would end up in a defecation anyway. Thus, Jesus declared that all kinds of foods were cleansed or made clean (καθαρίζων πάντα τὰ βρώματα). This would have been a major rejection of Jewish Torah law and the use of kosher food, since there was a major distinction between clean and unclean foods. This saying of Mark about no more unclean foods was not in Matthew who was writing to a Jewish Christian audience, but it is here for this gentile Christian audience. Luke omitted the whole question.
There is something similar to this in Mark, chapter 7:18-19. Jesus seemed a little upset that they still did not understand what he was telling them about defilement (ὁ δὲ εἶπεν Ἀκμὴν καὶ ὑμεῖς ἀσύνετοί ἐστε). He pointed out that they had to understand (ὐ νοεῖτε) that everything entering into the mouth (ὅτι πᾶν τὸ εἰσπορευόμενον εἰς τὸ στόμα) went into the stomach (εἰς τὴν κοιλίαν χωρεῖ). From the stomach, it came out in a bowel movement that ended up in a sewer, latrine, or dung heap (καὶ εἰς ἀφεδρῶνα ἐκβάλλεται). There was a famous saying that it is harder to sell corn after it has been eaten by a pig than before it was eaten. Whatever went into your mouth would end up as defecation.
There is something similar to this in Mark, chapter 7:15. Jesus, via Matthew, went back to the problem of impurity, unclean or defiled people. Thus, spiritual purity was more important that physical purity. It is not what you put into or what enters into your mouth (οὐ τὸ εἰσερχόμενον εἰς τὸ στόμα), such as unclean food, that pollutes or defiles a man or a person (κοινοῖ τὸν ἄνθρωπον). Rather, what comes out of your mouth (ἀλλὰ τὸ ἐκπορευόμενον ἐκ τοῦ στόματος τοῦτο), such as words, that defile, pollute or make a man or person unclean (κοινοῖ τὸν ἄνθρωπον). It is not what you put into your mouth that makes you unclean, it is what comes out of your mouth that makes you unclean or defiled.