A single deposit of $8,000 would not be "flagged" by the IRS. The IRS wouldn't even know about it.
I don't think it would cause any problems buying a house, either. When you say "apply for a house," do you mean apply for a mortgage? The lender is not likely to know about the deposit. They might ask the current balance in your checking account at the time that you apply, but they wouldn't look at past transactions.
But where does the $8,000 come from? And when you say "lump sum," do you mean that you are depositing cash? If the IRS has other reasons to think that you might be hiding income, they could audit you and look at your bank deposits. Then you would have to explain where the $8,000 came from, and why you did not report it as income. They would be particularly likely to ask about a large cash deposit if there is no record of where the cash came from.
