Please know that -- as others note below -- this is normal and quite typical. He is not being influenced to be "bad" by school, nor is anything "going on" there.
Moving to kindergarten is a bigger change for kids than we adults realize or remember. Even if he was in a great preschool, it was half-days three days a week; this is many more hours, with many more kids in the classroom (I assume), and with a stronger emphasis on "it's time to stop doing X and move to doing Y right NOW" that even the nicest teacher and most mellow classroom must still follow. He has to hold himself together and pay attention and be his best self all day, every day and it seems eternal to him.
At home, well-- you know the saying, "Familiarity breeds contempt," right? In this case, familiarity breeds -- not contempt, mom, but release. He has been holding himself in all day and when he gets home he's deflating like a balloon, letting out that perfectly normal tension. He becomes a grump and doesn't listen because all day long he has to be not a grump and a good little listener. When he fussed about how annoying it was to "do that all the time" with flush and wash -- he was told all day to do this and that (and probably to flush and wash there too). When you tell him to come in from play, he heard "Time to stop play and do XYZ" all day.
I'm not saying you need to stop directing him or reminding him of what's needed! No, you still must do that. But please be very patient. This is not really a case for discipline yet; don't fuss back at him or punish unless he really gets out of control. Try to ignore as much as you can at this time; if he is really disrespectful, try meeting it with a very chilly "I'm sorry you are talking that way; when you talk to me that way I can't talk with you" and leave the room rather than engaging with him any more. He wants your attention more than anything at this age, so removing your attention can be very effective.
Give him some more time. Also be SURE to give him a lot of down time immediately after school.
Some things that can help:
Have a snack ready for him IN the car when you get him; that can really help some kids because they often are ravenous and their blood sugar is dipping at the end of a school day, and a car snack both adds some fuel and, frankly, distracts them.
If he rides the bus: How long is the bus ride? That really can add to a kid's day and increase the grumpiness and puts more time between him and his down time and snack time; consider picking him up in the afternoons if you can instead. Not always doable but I think bus rides of more than a short distance can make younger kids' days too long if they are in full-day K.
Don't overdo it with eager questions about "How was your day? What did you do?" I was always guilty of that! We want to hear all about how they spent their time, what they liked, who their friends are...but they need a mental break immediately after school, so hold off and don't ask even well-meaning questions until later, or bring things up naturally at times like when you're reading to him -- what book did teacher read at circle time today? And so on.
If he has any minimal homework in K (some do), don't expect it to get done immediately after school but don't let it wait too late either. Get it done before dinnertime because he may fade too fast afterward.
If he has siblings, please be sure he gets time with you and/or dad without them around right after school. Don't expect him to play nicely with siblings (or even next door friends) immediately after school because he's been around other kids all day long. If he wants to blow off steam and run around and play with others, great, but don't expect too much in terms of playing together on anything.
Again, this really is typical and not a sign that something's wrong at school or that he suddenly dislikes home or is upset over something. His great behavior at break shows that. He is just learning to deal with the normal stress of going from preschool to full-time K. Try not to attach too much meaning to it or let it stress YOU too much or he will pick up on your stress with him and reflect it back with more acting out. Right now ignore what you can, remove yourself coolly whenever you can (more effective with many kids than yelling), and give him space and don't expect a lot of homework, or formal activities, immediately after school is done.