Plumbing Questions? Ask a Plumbing Expert.
Where the pipe exits the home, (generally through the rim joist.) it generally turns down with a 90 degree bend. Replace the 90 degree bend with a tee. On the top side of the tee, extend a riser up 2 feet and turn out with a 90 degree bend. This will act as an overflow.
Does your pipe exit the house as stated above?
If not, does the pipe exit the house underground?