Is it possible to keep the outlet pipe of portable air conditioner inside the house instead of putting it out through the window and what might be the disadvantage of doing so?

Give it a go and then you can share your results - i'd like to know how this woudl work also.

Personally, i think it still should work effectly, maybe a slight reduction in cooling/heating, but if the piping is has no leaks, i think it will work.

Just make sure the unit will never get wet through rain & use a weatherproof extension cord.

Good luck