First is the drain hose looped up[ about a foot higher than where it drains into the drain system. This reduces the chances that it will siphon stuff back out or the drain.

Have you changed your detergent or rinse aide type recently.
Is the heater working.
Have ypou drained some water out of the hot water tank. Use either the pressure releif or the drain on the bottom, let it run till it is nice and clear.

Here is a good link. Check out the last couple paragraphs.
http://www.applianceaid.com/drain_wash.html#sand