Don't wash them until just before you're ready to cook them
1) Look at the bottom of the stem of each and every morel. If dirty or tough-looking, CUT IT OFF.
2) Cut each morel in half lengthwise to expose the hollow center. Prepare a large bowl of salted water by adding 2 Tbsp to a gallon of cold water.
3) Soak in salted, cold water for about 40 minutes or up to 1 hour. Unlike many other mushrooms, morels do not readily soak up water. Wild morels come straight from the forest and their honeycomb structure can harbor grit and forest debris – not to mention the occasional creepy-crawly. The salted water is just the thing to convince any hitch hikers to move on.
4) Drain-Rinse-repeat (with unsalted water) until no grit remains.
5) If you skip step 1, step 4 will go on forever and you will still eat grit.
6) Spin morels dry in salad spinner.
The Johnson Family Cookbook