Recently we inspected a Sarasota home where the seller had installed a washing machine on the lanai. The drainage for this washer was inadequate. The drain line was run up and into the home, eventually meeting up with the sewer line somewhere. The problem with this setup is that when the washing machine pump stops pumping the dirty water out, all the dirty water in the line will run back into the machine.
The correct setup is to install a standpipe with an air gap that will not allow water to be siphoned back into the washing machine. There are additional requirements for standpipes. They’re height should not exceed 30 in and should not be less then 18 in. Also the trap is not allowed to be in the floor but rather should be elevated above the floor at least 6 in. This setup will allow water to drain properly from the washing machine without the risk of siphoning water back into the washing machine.