Simmer oysters in thier own juice for approx. 5-7 minutes, or until the edges begin to curl. Saute' peppers & celery in butter until tender. Blend in the flour, add the milk & cook stirring until the sauce thickens. Add the oysters, pimientos, the seasonings and stir them all together gently. Pour this into a buttered casserole, top with pie pastry & bake in 450 degree F pre-heated oven for 20 minutes or until the crust is brown.