Washing machine connected to sink issue.

baser999

Checked the outside drain hole?  Our sink and appliances discharge into the outside drain which has on the odd occasion become blocked with leaves despite there being a grate covering the hole. This obviously stops the water flowing away properly and so if there’s been heavy usage of appliances at the same time, it has backed up. We can sense when it may need checking as it ‘gurgles’ through the sink plug. Clear the leaves, all sorted. We know now to check it regularly 

kipsterno1

When you fit the washing machine pipe to the spigot check the instructions for the machine to see what height they recommended it should be. If it's to low water from the sink can flow back to the machine.

Mutton_Geoff

The washing machine hose is not connected properly. It should be clamped over a spigot (like you have unused on the opposite side) not just pushed in the hole. The end of the washing machine hose could be blocking the flow from sink to trap.

All that mess (and smell?) is caused by incorrect installation (ie it's currently a bodge).