If your washing machine has a black jelly-like substance growing in the soap dispenser it is likely to be a fungal/bacterial growth called biofilm. Apart from looking nasty, it can cause problems because it blocks up the little holes in the top of many soap dispensers where the water enters the washing machine. This can cause water flow to be restricted. Other problems can be that water is deflected into other compartments causing for example the fabric conditioner compartment to take the conditioner too soon, or even to not get flushed out at all. Finally, the deflected water can cause leaks as water is diverted or sprayed to the front of the dispenser and runs down from the bottom of the dispenser drawer.