Won't drain water it just builds up ins...

If you can find the drain line outside it probably is is white pvc or black polyurethane i use a wet vac. and secure it with tape so you get a better suction. If its upstairs there is probiably a second one so do both just incase. After time fungus builds up and can cause it to over flow try that see what you get out of it. if it doesnt work thetimnelson@yahoo.com